The color of normal skin is mainly determined by the following two factors: 1, the content of pigments in the skin: that is, melanin and carotene in the skin and the content of oxidized and reduced hemoglobin in the blood of the skin; 2, the anatomical differences in the skin: mainly the thickness of the skin, especially the thickness of the corneal and granular layers. The thin epidermis easily shows the color of blood in the dermal papillary vessels; the granular layer is thick, with poor light transmission and yellow skin color. Pathological skin color changes in addition to the above-mentioned several pigment content increase or decrease beyond the normal range, but also due to drugs (such as adipine, clofazimine), metals (such as gold, silver), foreign bodies (such as tattoos, powder particle deposition) and other metabolic products of the deposition (such as jaundice). It may also be caused by pathological changes in the skin, such as abnormal skin thickening, thinning, edema, inflammation, softening, necrosis, and other changes in skin color. Melanin is the main pigment that determines skin color, and its physiological function is to protect tissues from UV-induced damage, i.e. sunburn, aging, cancer, etc. The rationale for this protective effect is not fully understood, and it is currently believed that it is not simply a function of light absorption. In addition, whether melanin has other important physiological functions needs to be further investigated. Skin color shades, especially uneven color suppression, can cause cosmetic problems and cause mental burden.