Cognition of Color Shift in Leather Products and the Influence of Display Lighting of Luxury Goods

Abstract

The aim of this study is to investigate the influence of different LED colors on leather color shift to prevent misleading purchases. Six light sources consisting of three color temperatures (2700 K, 4000 K, and 6000 K) and two illuminances (750 lux and 1500 lux) were used. Red and brown leathers, common in the luxury goods market, with or without grain, were studied. The colors and patterns resulted in four leather surfaces for a color shift cognition experiment. The results indicated that: (1) Color temperature, illuminance, and leather color significantly affected color shift perception. (2) Two-factor combinations of color temperature and grain as well as color temperature and leather color generated interaction toward color shift. (3) The three-factor combination of color temperature, grain, and leather color also generated interaction toward color shift. The criticalness of factors affecting leather color shift was such that leather color > color temperature > illuminance > grain. The results can serve as references for the luxury goods and fashion industry in the management of retail display illumination and for color control of leather products under different illumination environments, thereby promoting the sustainability of leather product consumption.

1. Introduction

Through production methods, such as different approaches to cutting and surface treatment, leather is widely used for shoes, hats, fashion clothing, and luxury goods. As a branch of the fashion industry, leather products are often considered luxury products [1]. The emphasis the LVMH group placed on leather products and their acquisition of companies in this area highlighted the status of leather as a luxury good [2]. The trade in luxury goods has been increasing at a speed exceeding the consumption of other garments, turning luxury products into a critical component of the global economy [3]. Thus, leather consumption and trade will rapidly become more prominent [1].

Unlike consumers of regular products, consumers of luxury products care about not only functionality but also the two dimensions of consumption experience and symbolism [4]. Holbrook and Hirschman stated that product consumption must satisfy the consumer’s sensual enjoyment needs [5]. To promote revenues from leather products of luxury brands as well as to shape a favorable consumer experience to meet the sensual enjoyment needs of consumers, display lighting enabling visual experiences and perceptions is critical. Adequate display lighting in a fashion retail shop has positive meaning for consumers; it can increase the time consumers remain in the product display area [6]. Similarly, the display lighting at a shop can reinforce visual marketing effects [7]. Shops use visual marketing strategies to attract consumers and increase their purchase desire [8]. Consumer cognition about the price and quality of a product on display is affected by the color temperature of the product display lighting [9], and consumer cognition of the quality of a luxury good is a determining factor of the luxury brand image [3]. Therefore, lighting control and management of the retail market product display affect visual perception and thus the brand image of luxury products. Singh’s study uncovered that during the brief moment consumers first encountered a product, 60% of their evaluation of the product was based on the color of the product [10]. Thus, using display lighting to foreground the color and grains of leather products, making them look noble and gorgeous, has become the norm in luxury product shop lighting control and management. However, Dou et al. [11] discovered that the color temperature of the light source could generate a cognition bias about the color of the object under the light. If a visual marketing strategy that overlooks the faithful presentation of a leather product’s color characteristics is blindly pursued with inappropriate lighting, customers will misjudge the color of the leather and consequently make misguided purchases. If a wrongful purchase behavior occurs due to inappropriate lighting, after the consumer leaves the shop, they will have the feeling that the color of the product is different from that of the product on display. Thus, they cannot maintain a favorable sensual enjoyment and consumer experience, and they will not continue their purchase behavior, in turn having negative impressions toward the product and the related luxury brand and affecting the brand image and relevant market.

Therefore, managing the display light source at luxury goods shops is key to its impact on consumer cognition about leather product colors. To date, the display lighting in both luxury goods and general retail shops consists of the general lighting of the shop, vertical lighting, accent lighting, and scene projection lighting [12]. Shops often use accent or vertical lighting at a short distance, hoping to achieve a favorable display promotion effect. However, the most critical functions of display lighting are to present the true nature of a product, make it stand out, and rapidly grasp consumers’ attention, enabling them to precisely identify its characteristics [13]. However, leather is a material with complex characteristics. Its surface microstructure contains specific grain types, resulting in lighting reflection with specific luster and direction [14], thereby contributing to the uniqueness of lighting control in the display of leather.

A light-emitting diode (LED) has the advantages of low energy consumption, high performance, long service life, low maintenance cost, and easy adjustment [11]. As a result, it is widely used in display lighting in luxury products and common retail spaces. Businesses often use three aspects of LED lighting on display products, namely color rendering, illuminance, and color temperature. Regarding color rendering, Rea and Freyssinier stated that a color rendering index (CRI) or Ra > 80 enables people to perceive the colorfulness of a product [15]. The Illuminating Engineering Society suggested that the CRI at retail shops be at least 80–90 [16]. In fact, the color rendering of LED lights is predesigned before they leave the factory. Few studies have experimented with it as a control variable [17]. An LED’s illuminance and color temperature are also discovered to affect visual perception [18]. People’s sense of joy, awakeness, and feeling of control increases with illuminance. When people have a high sense of joy and awakeness, their sense of control over a space increases, which causes consumers to extend their stay in a consumption environment with increased chances of purchasing [19]. Soranzo et al. [20] discovered that the illuminance of a light source affects the identification of space and objects [20]. A higher color temperature is a colder light source color and is often used in offices to increase attention. A lower color temperature presents a warmer light source color, which is often used in public spaces, such as commercial spaces, to present a more relaxed spatial atmosphere [21]. A study supported the argument that color temperature and illuminance affect perceptions about the color of objects [22]. The color temperature of an LED affects people’s psychological state [23] and physiological needs [24].

LED illuminance and color temperature can not only cause errors in human color recognition, but also deceive intelligent computer vision systems [25,26]. In a study conducted by Koo et al. [27], they claimed that the picture of a human face captured by a camera in a low-illuminance environment is difficult to recognize. Fortunately, their study provides a new method to convert the image to a normal illumination version. However, in retailing display lighting, the color shift on products can only be solved by adjusting the lighting settings.

Specifically, the problem of lighting generating cognition bias about the appearance and color of leather products on display should be fully considered regarding LED display lighting control and management at shops selling luxury products. Specifically, adjusting LED color temperature and illuminance to the foreground color and grain of leather products and generating a favorable sensual experience using visual marketing to promote sales, while not misleading consumers by using lighting to avoid negative impressions about the product, shop, and brand, enables retailers to promote sustainable purchase behavior. These are problems worth researching for luxury product marketing and sales, purchase management, and brand image shaping and maintenance. However, existing studies of these areas are scarce.

Accordingly, this study discussed LED light sources on leathers by using combinations of color temperatures and illuminance that lead to cognition bias of leather color under the natural color system (NCS) ring regarding shifts in the three dimensions of blackness, saturation, and hue. The results may serve as references for luxury goods and fashion product sales marketing in controlling and managing the display light source for leather products.

2. Materials and Methods

2.1. Participant

The researchers recruited 15 volunteers. To ensure the effectiveness of the experiment, they underwent tests involving color blindness, color weakness, concentration and observation, and Snellen’s eye chart. The vision of both eyes of the 15 volunteers after correction was over 0.8 on the Snellen chart tests. None had color blindness, color weakness, or poor concentration and observation. The demographic data of the 15 participants were as follows: 8 men and 7 women, aged 22–53 years. Their mean age was 32.02 ± 8.32 years.

2.2. Experimental Design

2.2.1. LED Light Source Combinations

A physical store usually sets the color temperature of a product display light source at 2700 K–4000 K [28]. Color temperatures between 2700 K and 4000 K are in the “comfortable” area of the Kruithof curve [29]. Karlen et al. stated that the color temperature range of 2700–4000 K is suitable for homes, bars, shops, and display lighting, whereas that of 4100–6000 K can be used in special lighting situations where color identification is critical [30]. In this study, color temperatures of warm (2700 K), neutral (4000 K), and cool (6000 K) were selected. To ensure color rendering, LED lights with Ra = 85 when they were manufactured were selected.

According to the Chinese National Standards of Illumination and to the Japanese Industrial Standards, 750 lux is suitable for large department stores, wholesale stores, clothing stores, high-end specialty stationery stores, and other stores, whereas 1500 lux is recommended for counters, displays, and windows. Thus, the two illuminances of 750 lux and 1500 lux were selected for the experiment.

2.2.2. Objects for Measurement

Previous studies indicated that 11 leather colors were common, but the two most popular among women were black and red [3]. In comparison, the most common colors on the market were black and brown. For grain, litchi was most commonly used on the surface of fashion bags [31]. Chen et al. sampled preferences of leather colors and discovered that the most popular was white, followed by black, red, and brown. For grain, small litchi grain was most popular, followed by smooth, medium litchi grain, large litchi grain, and floater [32]. The purpose of this study is to investigate the influence of different LED colors on leather color shift to prevent misleading purchases. Therefore, the research subject should focus on the most popular leather colors on the market. According to Tien-Li Chen et al. [32]’s study, leather samples of white, black, red, brown, and small lychee-grain and smooth, untextured surfaces of each color were selected from the same supplier for color cognitive bias testing. Using an NCS Colourpin-II reader to read the color, the NCS values of four color samples were S0300-N white, S9000-N black, S3060-R red, S5030-Y60R brown. However, in the process of color reading, the color of white leather was not evenly painted, and the values in some areas of the sample showed s0500-N white. At the same time, in the pre-test, no matter what kind of light source the black leather was irradiated with, there was no significant color bias cognition phenomenon. Compared with this study, it was meaningless to discuss the color bias of the leather under the LED light. In addition, the uneven painting of white leather will affect the experimental results. Based on the aforementioned findings, a color cognition bias experiment was designed for black, red, and brown leathers. However, during pre-testing, regardless of the light source, black leather did not yield significant color bias cognition and was, thus, irrelevant to our research purposes. After discussion with experts and consideration of the evenness in spray paint in relation to lighting, products from the same supplier were selected. The supplier provided four leather samples, two of red S3060-R and two of brown S5030-Y60R, under the NCS system. Their surfaces were small litchi grain or smooth and without grain with matte spray paint (Figure 1). Their sizes were 3 cm × 6 cm. Their surface gloss unit (GU) values are shown in

Table 1. GU of the surface of the selected leather.

Color	Texture	Light Source Angle	Gloss (GU)
Red	No grain	60°	5.6
	Grain		4.2
Brown	No grain		5.3
	Grain		4.1
Red	No grain	80°	4.8
	Grain		3.7
Brown	No grain		4.7
	Grain		3.1

. After a comparison of the color tickets, red S3060-R and brown S5030-Y60R were used as the centers. In the dimensions of blackness, saturation, and hue, extensions were made in positive and negative directions (Figure 2 and Figure 3). Then, from the NCS system, 12 color tickets were selected for comparison (Figure 4).

2.2.3. Variables

The independent variables were LED color temperature, illuminance, leather color, and leather grain (

Table 2. Experimental variables.

Independent Variable	Level
Correlated color temperature	2700 K
	4000 K
	6000 K
Illuminance	750 lux
	1500 lux
Grains	No grains
	Grains
Color	Red
	Brown

). The dependent variables were the saturation, blackness, and hue of the leather materials.

2.2.4. Lightbox Design

To meet the experimental requirements, a custom wooden lightbox that met the TILO-D65 standard for a light source was constructed. Its specifications were 710 cm × 570 cm × 400 cm (width × height × internal depth). Black light-absorbing materials were pasted to the internal sides of the box to avoid the reflection of the light source affecting the results. On the top of the box, a set of LED light beads that could illuminate six types of light, namely 2700 K × 750 lux, 2700 K × 1500 lux, 4000 K × 750 lux, 4000 K × 1500 lux, 6000 K × 750 lux, and 6000 K × 1500 lux, was installed. They shone vertically down on the object under inspection (Figure 5).

2.3. Steps

The experiment was conducted in an independent laboratory without light hazards. The eyes of the participants were approximately 43 cm from the lightbox. Before the experiment, the researchers explained the experimental purposes and steps. The participants had to compare the color of the object in the box in the left (four combinations of colors, red or brown, and grain, with or without) under six combinations of color temperature and illuminance against the color tickets in the box to the right (under a TILO-D65 standard light source). Then, they had to select the color ticket most similar to the leather stimulus in the LED box on the left. The researchers would subsequently record and analyze the blackness, saturation, and hue of the color ticket selected by the participant. Although the experiment was not timed, to avoid learning effects and visual fatigue interfering with the results, participants were asked to complete the tests as quickly as possible. After they completed the test for each color temperature and illuminance combination, they were asked to take a 5 min break outside the experiment room. When the participant was away, the researchers randomly rearranged the color tickets for the next light source combination test.

3. Results

The 15 participants selected color tickets under 24 conditions involving three color temperatures, two illuminances, two surface grain conditions, and two colors. Under each experimental condition, the values of blackness, saturation, and hue of the selected color ticket minus the values of those of the leather stimulus represented color shift differences. After the values were recorded and organized, a multivariate analysis of variance (MANOVA) was conducted.

The results (

Table 3. Results of MANOVA.

Independent Variable	F	Sig.	Eta Squared
Correlated color temperature	25.358	0.000	0.186
Illuminance	7.27	0.000	0.061
Colors	63.258	0.000	0.362
Grains	2.922	0.034	0.026
Correlated color temperature * Grains	2.948	0.008	0.026
Correlated color temperature * Color	9.078	0.000	0.075
Correlated color temperature * Grains * Color	2.419	0.025	0.021

) indicated that changes in the four independent variables (i.e., color temperature, illuminance, color, and grain) resulted in significant color shift differences. On the basis of eta squared values, the degree of correlation between the independent variables and the leather color shift was, in descending order, color, color temperature, illuminance, and grain. The results (

Table 4. Results of the tests of between-subject effects.

Independent Variable	Dependent Variable	F	Sig.
Correlated color temperature	Blackness	38.271	0.000
	Saturation	80.859	0.000
	Hue	4.662	0.010
Illuminance	Blackness	17.614	0.000
	Saturation	8.960	0.003
Color	Blackness	41.413	0.000
	Saturation	138.915	0.000
	Hue	52.036	00.000
Correlated color temperature * Grains	Blackness	4.390	0.013
	Saturation	7.149	0.001
Correlated color temperature * Color	Blackness	16.812	0.000
Correlated color temperature * Grains * Color	Blackness	5.547	0.004
	Saturation	4.594	0.011

) indicated that color temperature and leather color most significantly affected blackness, saturation, and hue, whereas illuminance significantly affected blackness and saturation. Grain had no significant effect on blackness, saturation, or hue. However, grain and color temperature exhibited a two-factor interaction with blackness and saturation. Color temperature and color also exhibited a two-factor interaction with blackness. Color temperature, grain, and color exhibited a three-factor interaction with blackness and saturation. To discuss color shift trends in blackness, saturation, and hue for each independent variable under different control conditions, a one-way analysis of variance of the independent variables was conducted.

3.1. Color Led to Color Shift

For both red and brown leathers, as color temperature, illuminance, and grain were changed, significant color shifts were observed for their blackness, saturation, and hue (Appendix A). Regarding blackness, seven control conditions yielded significant differences, namely 2700 K × 1500 lux × grain, 4000 K × 750 lux × grain, 4000 K × 1500 lux × grain, 6000 K × 750 lux × grain, 6000 K × 750 lux × no grain, 6000 K × 1500 lux × grain, and 6000 K × 1500 lux × no grain. Overall, regardless of the light source or presence of grain, the direction of the color shifts in the blackness of brown leather was consistent—they all became lighter. For red leather, under different lighting, different color shifts were observed. Under a high color temperature of 6000 K, the overall blackness color shift was darker. Under the medium color temperature of 4000 K and with grain, the blackness also became darker. However, under the low color temperature of 2700 K and under the medium color temperature of 4000 K without grain, the blackness of the red leather became lighter. This phenomenon verified the results in Table 4, that color had a subjective effect on blackness, that color temperature and grain had a two-factor interaction with blackness, and that color, color temperature, and grain had a three-factor interaction with blackness.

In addition, under the nine control conditions of color temperature, illuminance, and grain, red and brown leathers exhibited significant differences in their saturation color shift, namely 2700 K × 750 lux × no grain, 2700 K × 750 lux × grain, 4000 K × 750 lux × grain, 4000 K × 1500 lux × grain, 4000 K × 1500 lux × no grain, 6000 K × 750 lux × grain, 6000 K × 750 lux × no grain, 6000 K × 1500 lux × grain, and 6000 K × 1500 lux × no grain. Judging from the mean value of the color shift under various control conditions, regardless of the light source or surface grain, brown leather exhibited a consistent trend of increased saturation in color shift. However, for red leather, color temperature and grain led to different changes (increase or decrease) in saturation. Under a low color temperature of 2700 K, regardless of the presence of grain or the illuminance, the red leather exhibited increased saturation. Under a medium color temperature of 4000 K, the red leather without grain had increased saturation, whereas the red leather with grain displayed reduced saturation. When the color temperature was 6000 K, the red leather exhibited reduced saturation under every condition. These observations verified the results in Table 4: color had a subjective effect on saturation, color, and color temperature, and grain had a three-factor interaction effect on saturation.

The mean of the color shift value for hue was negative. As mentioned, in analyzing the relationship between the hue of the leather sample color in the NCS system and the comparison of the hue value of the color tickets, red and brown both shifted leftward toward yellow. Furthermore, under the five control conditions of 2700 K × 1500 lux × no grain, 4000 K × 750 lux × grain, 4000 K × 1500 lux × no grain, 6000 K × 1500 lux × grain, and 6000 K × 1500 lux × no grain, the shift distance of red and brown colors exhibited significant differences; the color shift distance of brown was greater than that of red. This verified the result in Table 4 regarding the subjective effect of color on hue.

3.2. Color Temperature Led to Color Shift

Leather color shifts were compared under different color temperatures using eight controlled conditions of the combinations of two colors, two illuminances, and with/without grain. Color temperature change significantly affected the color shift in blackness, saturation, and hue. Appendix B presents the changes from a low color temperature of 2700 K to a high color temperature of 6000 K. Red leather had significant color shifts in blackness, saturation, and hue.

Regarding blackness, in general, a high color temperature led to high blackness, and vice versa. Under a medium color temperature of 4000 K, when the leather surface had grain, regardless of the illumination, the blackness of the red leather increased. The color shift value was close to that of the high color temperature of 6000 K and had no significant difference compared to it. When the leather surface was smooth (without grain), under a medium color temperature of 4000 K, regardless of the illuminance, the red leather exhibited reduced blackness. Under an illuminance of 750 lux, its shift in blackness was not significantly different from that under 2700 K. Under an illuminance of 1500 lux, it was significantly lighter than under 6000 K and significantly darker than under 2700 K. Regarding saturation, the effects of the three color temperatures on the color shift of the red leather were significantly different regardless of the illuminance or the presence of grain. Overall, a low color temperature of 2700 K resulted in increased saturation, and a high color temperature of 6000 K reduced saturation. Under a medium color temperature of 4000 K, when the leather surface had grain, regardless of the illuminance, the red leather displayed decreased saturation, which did not significantly differ from that under 6000 K. However, when the leather surface had no grain, under 4000 K, regardless of the illuminance, the saturation of the red leather increased, and the shift in saturation was not significantly different from under 2700 K. Regarding hue, under the three color temperatures, only under a high illuminance of 1500 lux and with grain did the red leather exhibit a significant shift. In sum, the red leather shifted the largest distance toward yellow under 2700 K, and the smallest distance under 6000 K. One-way analysis of variance post-hoc results revealed that the shift under a medium color temperature (4000 K) was nonsignificant when compared with a low or high color temperature.

For brown leather, the color shifts under the three color temperatures did not differ significantly in blackness and hue (Appendix B). For saturation, regardless of the illuminance or the presence of grain, the shifts were significantly different. Regarding the saturation of red leather, the shift under different color temperatures could increase or decrease. By contrast, the saturation shifts for brown leather were in the same direction (increasing). Regarding the degree of shift, the shift was the greatest under 2700 K, followed by 4000 K and 2700 K. Under an illuminance of 750 lux without grain, the difference in the distance under three color temperature shifts was such that 2700 K > 4000 K > 6000 K. Under the same illuminance without grain, the shifts in saturation under 4000 K and 6000 K were not significant, but they were both significantly smaller than that under 2700 K. Under illuminance of 1500 lux and with grain, the difference of the shift distance under three color temperatures was such that 2700 K > 4000 K > 6000 K. Under the same illuminance without grain, the shifts in saturation under 4000 K and 2700 K were nonsignificant, but they were both significantly greater than that under 6000 K.

The color shifts under the three color temperatures verified the interaction effects and the subjective effects of color temperature on leather colors regarding blackness, saturation, and hue in Table 4.

3.3. Color Shift Caused by Illuminance

Leather color shift was compared under different levels of illuminance (

Table 5. Differences in color shifts caused by level of illuminance.

Dependent Variables	Illuminance	Colors	CCT	Grains	Mean (SD)	F	p-Value
Blackness	750 lux	Red	2700 K	Grains	−3.67 (6.67)	4.568	0.041
	1500 lux				−8.00 (4.14)
	750 lux		6000 K	No grain	9.33 (2.58)	5.227	0.029
	1500 lux				4.67 (7.43)
Saturation	750 lux	Red	6000 K	No grain	−9.33 (2.58)	5.227	0.029
	1500 lux				−4.67 (7.43)
Hue	750 lux	Brown	6000 K	No grain	−6.67 (4.89)	7.000	0.013
	1500 lux				−10.00 (0.00)

). For red leather, only under 2700 K with grain did 750 lux and 1500 lux cause a significant shift in blackness. Regarding saturation, a significant shift was only observed under 6000 K without grain. For brown leather, different illuminances only produced significantly different effects on shifts in hue under 6000 K without grain.

For red leather, on the basis that low color temperature reduced blackness, a high illuminance of 1500 lux created a greater shift in blackness than did a low illuminance. In other words, compared with 750 lux, 1500 lux exhibited a lighter blackness under 2700 K and under 6000 K.

Therefore, illuminance did not significantly affect the blackness of red leather. A high illuminance of 1500 lux, compared with a low illuminance of 750 lux, resulted in a lighter blackness. However, under a medium color temperature of 4000 K, regardless of with or without grain, no significant shift was observed. Regarding the shift in saturation for red leather, changes in illuminance did not affect the direction of the shift for saturation. Compared with 750 lux, 1500 lux had higher saturation. However, under 2700 K and 4000 K, regardless of with or without grain, the shifts in saturation caused by the difference in illuminance were nonsignificant.

Regarding the impact of illuminance on the shift in hue, significant differences were observed only for brown leather under 750 lux and 1500 lux under a color temperature of 6000 K without grain. Specifically, the shift distance under 750 lux was significantly smaller than that for 1500 lux. Under other conditions, the shifts in hue caused by these two illuminances were nonsignificant.

The two illuminances did not generate significant differences in color shift under the same color, same color temperature, or different leather surface, nor did they generate significant differences in color shift under different color temperatures with the presence/absence of grain and the same color. Moreover, they did not generate significantly different color shifts regarding different colors under the same color temperature and the presence/absence of grain. Therefore, illuminance did not have an interactive effect with the other independent variables, which was consistent with the results in Table 4.

3.4. Grain

Only under a medium color temperature of 4000 K did grain exhibit a significant difference in the shift for blackness and saturation for red leather (

Table 6. Differences in color shifts for grain.

Dependent Variables	Grains	Colors	CCT	Illuminance	Mean (SD)	F	p-Value
Blackness	NO grain	Red	4000 K	750 lux	−1.00 (7.12)	7.447	0.011
	grains				5.67 (6.23)
Saturation	NO grain	Red	4000 K	750 lux	2.67 (5.94)	12.600	0.001
	grains				−5.33 (6.40)
	NO grain		4000 K	1500 lux	2.00 (6.76)	4.350	0.046
	grains				−3.33 (7.24)

). A significantly different shift was observed under 4000 K and 750 lux, with the blackness of red leather without grain and with grain becoming lighter and darker, respectively. However, for other color temperatures, illuminances, and for black leather, grain or lack thereof did not significantly affect the shift in blackness.

Under 4000 K, regardless of the illuminance, the red leather without grain had an increase in saturation, but the degrees of increase did not differ significantly. Under the same situation, the saturation for red leather with grain was reduced, but the differences were not significant. However, as mentioned, the difference in the shift with or without grain was significant.

Overall, regardless of the color temperature or illuminance, the color shift generated for brown leather with or without grain had no significant difference. For red leather, the shift in blackness only reached a significant difference under 4000 K and 750 lux. For saturation, significant differences were observed under 4000 K, 750 lux and 4000 K, and 1500 lux. Therefore, relative to color, color temperature, and illuminance, grain had the smallest impact on leather color shift.

4. Discussion

This study discussed the color shift and trends of leather, a major material in luxury goods, that had or did not have grain, under different color temperatures and illuminances from an LED light source. LED lighting significantly affected the cognition of leather color with or without surface grain. Color and color temperature exhibited significant impacts on color shift regarding the blackness, saturation, and hue of leather materials. Illuminance significantly affected blackness and saturation, whereas grain did not have a major effect on color shift. However, through the color temperature as well as through the interaction between color temperature and color, grain exhibited a significant influence on leather color shift. Of the eta squared values in Table 4, η² of color = 0.362, and η² of color temperature = 0.186. According to the assessment standards of Cohen [33], color and color temperature were highly correlated with a color shift in leather, illuminance (η² = 0.061) was moderately correlated, and grain (η² = 0.026) had a low correlation. Therefore, the degree of correlation of the four independent variables with leather color shift was such that color > color temperature > illuminance > grain.

Overall, under the six combinations of color temperature and illuminance, brown leather exhibited a color shift toward yellow. However, the shift did not exceed one unit on the NCS color ring. When the color temperature was 6000 K, and when no grain was present, the color shift in hue exhibited significant differences. Specifically, under high illuminance of 1500 lux, the shift in hue was large and achieved a one-unit shift toward yellow. The presence of grain did not result in significant differences in shifts in the blackness, saturation, or hue of brown leather. The three levels of color temperatures also did not exhibit significant differences in shifts in the blackness and hue of brown leather. Only for hue were significant differences in color shift observed. Compared with high color temperature, low color temperature resulted in a greater increase in saturation. For medium color temperature, depending on illuminance and the presence of grain, different trends were observed: the color shifts in low and high color temperatures might be less prominent, or the shifts in low and high color temperatures may exhibit significant differences.

Under six types of light sources, the hue of red leather also shifted toward yellow. The overall shifting distance for hue was smaller than that for brown leather, and the shift was smaller than one unit on the NCS color ring. This may be because human eyes are less sensitive to red. The experimental results of Dou et al. [11] support this finding. Grain and illuminance did not have significant effects on the color shift of the hue of red leather. For color temperature, when under 1500 lux of illuminance and with grain, the shift under 2700 K was significantly larger than that under 6000 K. The differences between the shifts under 4000 K and 2700 K as well as between 4000 K and 6000 K were nonsignificant.

Regarding blackness, for red leather, a low color temperature reduced its blackness, whereas a high color temperature increased its blackness. Regardless of the illuminance or presence/absence of grain, changes in color temperature significantly affected the blackness of red leather. Judging from the changes of the two illuminances for color temperature, color, and grain, illuminance did not change the direction of the shift in the blackness of the red leather. However, compared with a low illuminance of 750 lux, a high illuminance of 1500 lux presented a lighter blackness. Specifically, under a low color temperature of 2700 K with grain, compared with 750 lux, 1500 lux exhibited a greater reduction in blackness. Under a high color temperature of 6000 K and without grain, compared with 750 lux, 1500 lux had a smaller increase in blackness. Notably, under 4000 K and 450 lux, grain significantly affected the differences in the shift in blackness. Specifically, grain caused a greater increase in blackness. Judging from the mean values of blackness shifts, the light source with the smallest influence on the blackness of the red leather without grain was 4000 K × 750 lux. The light sources with the smallest influence on the blackness of the red leather with grain were 4000 K × 1500 lux and 6000 K × 1500 lux.

Regarding saturation, for red leather, significant differences in saturation shift were observed, whatever the illuminance was and with/without grain. Overall, a low color temperature resulted in increased saturation, and a high color temperature resulted in decreased saturation. The saturation shift under a medium color temperature, which was affected by grain, was nonsignificant relative to that of low or high color temperature. The influence of illuminance was only significant under 6000 K and without grain. Thus, compared with 1500 lux, 750 lux resulted in greater saturation reduction. For grain under 4000 K, regardless of the illuminance, grain exhibited significant differences in saturation.

Regarding the GU of the leather sample surface, under 60° of illumination and 80° of illumination, the differences in GU values of brown and red leathers with or without grain were less than two units. This may be because the samples had undergone surface treatment into matte; thus, the grain level of the samples had a small influence on color shift. However, the GU values of leather that had a coarse surface and grain were lower than those with a smooth surface and no grain (Table 1). Under the same color temperature and illuminance, leather with a low GU (with grain) had a darker blackness and lower saturation compared with leather with a high GU (without grain; Table 6). A possible explanation may be that the low GU of leather with grain resulted in a low reflection rate in the direction of the light source, leading to a trend of decreased leather brightness and saturation. This explanation is consistent with the findings of Wu et al. [34,35].

4.1. Suggestions for Light Sources for Leather Product Displays

Based on the experimental results and analysis, the color shift differences in blackness, saturation, and hue for red and brown leathers are large, and retailers are advised against putting red and brown leather products on display under the same light source. In addition, to precisely present the color of leathers, light source combinations resulting in the lowest degree of the color shift should be selected.

According to the influence trends of color temperature and illumination for the blackness, saturation, and hue of leather colors, to avoid large increases or reductions in blackness or saturation and a large shift in hue (and thus the light source causing mistaken cognition regarding leather color). The display light of red leather should be chosen carefully. For example, if the color temperature of 2700 K is selected, the color of red leather will show a significant shift trend towards yellow. Another example is that the color temperature of 6000 K will lead to an increase in the blackness of red leather, especially under the 750 lux illumination, there will be a relatively significant darkening. This can have apparent color cognition misdirect to consumers. For red leather, selecting a light source of 4000 K × 750 lux for leathers without grain and a light source of 4000 K × 1500 lux for leathers with grain can make blackness and saturation more accurate. Under 4000 K × 750 lux, grain significantly affected the blackness and saturation of red leather. Therefore, red leather products with or without grain should be placed under separate light sources. In addition, although 6000 K caused the smallest shift in hue, it caused a greater shift in blackness and saturation than did 4000 K. Furthermore, differences for the shift in hue under 4000 K and 6000 K were not substantial. Therefore, a light source with a medium color temperature is more suitable for displaying red leather products.

Six different light sources did not result in significant differences in the shift in blackness for brown leathers. Judging from the mean values of the shift in saturation and hue, 6000 K × 750 lux caused the smallest shift for brown leather with or without grain. Therefore, this light source can precisely present the color of brown leather.

4.2. Limitations and Future Suggestions

Due to technical problems, obtaining samples of evenly painted glossy leather samples and green and white leather samples was unfeasible. Therefore, experiments for them were not conducted, and our study of the surface features of leather products was incomprehensive. Future studies should include glossy leather and leathers of other colors.

5. Conclusions

This study involved 15 participants aged 22–53 years (mean age 32.02 years); this wide range made the results representative. A total of 24 sets of color shift tests were conducted with each, involving three color temperatures, two illuminances, two surface types, and two colors of leather. The results indicated that a low color temperature increased saturation more than a high color temperature. In addition, only illuminance significantly affected the hue, and the impact was limited. Grain changed only the significance of the difference in saturation between the medium color temperature and the high and low color temperatures. Therefore, for the display lighting of luxury goods and fashion products, retailers should carefully consider whether they want to place red and brown leather products under the same lighting in case they generate unexpected results. Red leather products with grain should not be displayed with red leather products without grain under 4000 K LED lighting to avoid a significant color shift of the two, thereby confusing consumers.

For luxury products and fashion products with red or brown leather, the following types of LED light sources should be used: 4000 K × 1500 lux, 4000 K × 750 lux, or 6000 K × 750 lux. To display red leather products with grain, 4000 K × 1500 lux is suggested. For red leather products without grain, 4000 K × 750 lux is advised. For brown leather, 6000 K × 750 lux is recommended. With this approach, when consumers purchase leather products, their color shift cognition is reliable, and the color display of products is accurate. Thus, the brand image and consumption experience for luxury and fashion products can be maintained, promoting sustainable consumption of leather products.