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Hair color is the pigmentation of hair follicles due to two types of melanin: eumelanin and pheomelanin. Generally, if more eumelanin is present, the colour of the hair is darker; if less eumelanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair colour to change, and it is possible to have hair follicles of more than one color on the same person. Particular hair colours are associated with ethnic groups. The shades of human hair color are assessed using the Fischer–Saller scale. The Fischer–Saller scale, named after Eugen Fischer and Karl Saller, is used in physical anthropology and medicine to determine the shades of hair colour. The scale uses the following designations: A (very light blond), B to E (light blond), F to L (blond), M to O (dark blond), P to T (light brown to brown), U to Y (dark brown/black) and Roman numerals I to IV (red) and V to VI (red blond).〔(【引用サイトリンク】title=Change in Hair Pigmentation in Children from Birth to 5 Years in a European Population (Longitudinal Study) )〕 Its older version was Fischer scale. See also the Martin–Schultz scale or Martin scale for eye color. ==Genetics and biochemistry of hair colour== Two types of pigment give hair its colour: eumelanin and pheomelanin. Pheomelanin colours hair orange and red. All humans have some pheomelanin in their hair. Eumelanin, which has two subtypes of black or brown, determines the darkness of the hair colour. A low concentration of brown eumelanin results in blond hair, whereas a higher concentration of brown eumelanin results in brown hair. High amounts of black eumelanin result in black hair, while low concentrations result in gray hair. Pheomelanin is more chemically stable than black eumelanin, but less chemically stable than brown eumelanin, so it breaks down more slowly when oxidized. This is why bleach gives darker hair a reddish tinge during the artificial colouring process. As the pheomelanin continues to break down, the hair will gradually become red, then orange, then yellow, and finally white. The genetics of hair colors are not yet firmly established. According to one theory, at least two gene pairs control human hair color. One phenotype (brown/blonde) has a dominant brown allele and a recessive blond allele. A person with a brown allele will have brown hair; a person with no brown alleles will be blond. This explains why two brown-haired parents can produce a blond-haired child. However, this can only be possible if both parent are heterozygous in hair color- meaning that both of them have one dominant brown hair allele and one recessive allele for blond hair but as dominant always wins the parents both have brown hair. In a punnet square it is possible to determine the possibility of a certain trait in an offspring. The other gene pair is a non-red/red pair, where the non-red allele (which suppresses production of pheomelanin) is dominant and the allele for red hair is recessive. A person with two copies of the red-haired allele will have red hair. The two-gene model does not account for all possible shades of brown, blond, or red (for example, platinum blond versus dark blond/light brown), nor does it explain why hair color sometimes darkens as a person ages. Several gene pairs control the light versus dark hair color in a cumulative effect. A person's genotype for a multifactorial trait can interact with environment to produce varying phenotypes (see quantitative trait locus). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Human hair color」の詳細全文を読む スポンサード リンク
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