Skin color is an important factor related to judgment such as age, health condition, face impression, etc. It is very important to clarify its perceptual characteristics. Previous studies have reported that people show high sensitivity to changes in redness of the skin and that reddish skin looks brighter. From these facts, it is conceivable that people may recognize the skin and perceive the color of the skin. In this study, we focused on the relationship between the color distribution of skin color and color discrimination in particular. Principal component analysis was performed on the CIELAB value obtained by measuring the skin of 694 Japanese women and a color plane peculiar to the skin color composed of the first principal component and the second principal component was constructed. Then, the skin image and the monochromatic stimulus were modulated in eight directions on the plane, and the discrimination threshold was examined. We also examined the correspondence between the modulation direction and the change in the amount of melanin and hemoglobin which is the main pigment component consisting skin color. As a result, it was suggested that people have better discrimination for changes in color accompanying increase of hemoglobin.

　The blood in veins is red. Then why do veins appear blue? This is one of the "frequently asked questions" on colors. It seems that there are two typical answers to this question. One is that vein is not physically blue. Blue vein is just an illusion(the illusion theory).The other is that vein is physically blue because the blue light tends to be strongly scattered in the skin(the scattering theory).Which theory is correct? To solve this problem, we measured the colors of human arm veins and the Mongolian spot, that also appears blues, by using spectrophotometry. Then, we confirmed that both vein and Mongolian spot were not physically blue. Compared to the surrounding skin colors, they have low lightness and low chroma, but their hues were yellow-red, not blue. Therefore, these results qualitatively support the vein illusion theory. However, what kind of illusion mechanism works should be answered in the future.

　People are frequently aware of our face and its skin in the daily lives. Therefore, their appearance has been an important research subject in some academic and industrial fields such as color science, vision, and cosmetics. Color of the skin is one of the key factors when traits of their appearance are discussed. Consequently, plenty of studies on the skin color and facial complexion have been enthusiastically carried out with taking into account unique physical and perceptual properties of the skin and face. Some of these studies clarified that color of the skin and face possesses interesting and peculiar secrets that are little known in other objects. Evaluation of skin chromophores such as melanin and hemoglobin is also important, especially when the skin appearance is discussed from the standpoint of skin physiology. For the purpose of this aspect, useful methods to quantify the level of skin choromophores from spectral reflectance data or spectral/RGB images were proposed. These methods have been contributing to deepening the comprehension of skin appearance. In this paper, some of interesting knowledge reported in the previous studies relating skin color and facial complexion, and methods for the quantification of skin chromophores are reviewed.