Physically, color is the most intuitive landscape element in visual perception [10]. Due to the mechanisms of human visual perception, color contrast is considered to provide the most obvious and noticeable difference in environmental perception, especially in terms of visual detection thresholds [9]. Thus, color has a tremendous impact on the “quality of appearance” of design and even on human physiological health [11]. However, despite the increasing number of studies pointing to the importance of color in environmental perception, there is still a lack of research to support color selection in guiding design practice [12].

On a psychological level, color also has a significant impact on the subjective emotions of visitors. Red space corresponds to joy and passion and blue space corresponds to sadness, and these colors will prompt the crowd to produce corresponding behavioral feedback to the space [13]. Moreover, since environmental landscape color is a man-made product, the existing color environment not only reflects the humanistic inference of the designer, but also causes the audience to change their inner emotions and aesthetic feelings [14]. Existing studies point out that in signage design, colors are more likely to achieve visual harmony when there is little chromaticity or a large difference in luminance [11]. Brightness differences have a stronger effect on harmony and legibility, while chromaticity has a lesser effect [15]. Different gender labels affect the degree of subjective preference for color and the response to the environment [16]. In addition, extracting colors according to the local environment can help enhance the harmony of sign design [17]. The review shows that color significantly affects the visual appeal, subjective preference, and visual harmony of environmental signage design, but few articles discuss the quantitative relationship between gaze behavior and subjective preference.

Current global research on materials focuses on physical properties, such as environmental friendliness, durability, etc. Regarding physical properties, it has been pointed out that the selection of materials should be based on the unique local ecological environment and physical facility conditions [18]. In recent years, scholars focused on the introduction of life cycle assessment into material selection began to pay attention to material sustainability [19,20], such as recyclable design, biodegradability, and disassembly design, so that economic development and the ecological environment can coexist in harmony [21,22].

In terms of emotional properties, materials possess symbolic qualities. In facility design, materials constitute people’s memories of culture and place [23]. And, in the context of rapid urbanization, traditional materials are beneficial in addressing the serious homogenization and weakening of the cultural landscape in localities [24]. In addition, there are gender differences in material preferences, with women preferring recyclable and green materials [25]. Therefore, the choice of materials must fully account for users’ physical and psycho-emotional needs [18]. However, there are fewer studies on subjective preferences and visual attributes due to the wide variety of materials and the difficulty in conducting a controlled variable analysis. This gap exists in the academic literature.

In recent years, eye tracking, a technology that records human visual data to measure human behavior and psychology, has become an integral approach for examining how people perceive their surroundings [26,27]. Quartier et al. suggest that color is an essential element in the design of interior living spaces that impacts mood and spatial perception [28]. Bogucka researched the preferences for interior spaces with varying proportions, lighting, and color schemes and discovered that soft hues could induce favorable emotions in humans [29]. Chen et al. pointed out that people prefer to look at trees rather than buildings in outdoor activities [30]. Song investigated color preferences in dental hospitals and found that brown stabilized patients more effectively than the traditional blue [31]. Zhang discovered that subway rooms with too much or too little color saturation and brightness might be unsettling, and the most popular colors are not always the most visually pleasing for people [13].

Regarding gaze behavior, the Suarez study indicated that neither the path taken to examine the building nor the route’s starting point affected the time participants spent viewing various architectural components, and those architectural components that the participants deemed aesthetically attractive were noticed for a longer duration [26]. According to the research of Li et al., most people were drawn to text in landscape photographs [32]. Rusnak assessed the visual reaction skills of experts and found that they could perform a fundamental analysis but could not predict more complex responses [9]. Regarding gender differences, Sargezeh et al. found that females exhibited more exploratory gaze behaviors, as evidenced by greater eye-hopping amplitude and longer scan paths [33]. Through the existing literature, current empirical research guided by stress recovery theory (SRT) [34] and attention restoration theory (ART) [35] has focused on stimulus-driven bottom-up processes while experiencing nature. However, a comprehensive evaluation of the signage system is based on the bottom-up visual gaze process and the top-down subjective preference factor, and the correlation between the two deserves further study [36].

Although there has been much research on color in environmental space, there is a need for additional research on elements (substance and size). Due to the limitations of research methods and the number of investigations, it is challenging to undertake variable studies on morphology, but it is easier to conduct quantitative research on the change of color and material [9]. 

4. Practical Implications