Human hair color 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 the environment to produce varying phenotypes (see quantitative trait locus). Natural hair color can be brown, blond, black, red, or white; all natural hair colors including grey, white and lightest blond, are shades of brown. The Fischer–Saller scale, named after Eugen Fischer and , is
Eugen Fischer Eugen Fischer Eugen Fischer (5 July 1874 – 9 July 1967) was a German professor of medicine, anthropology, and eugenics, and a member of the Nazi Party. He served as director of the Kaiser Wilhelm Institute of Anthropology, Human Heredity, and Eugenics, and also served as rector of the Frederick William University of Berlin. Fischer's ideas informed the Nuremberg Laws of 1935 which served to justify the Nazi Party's belief in German racial superiority. Adolf Hitler read Fischer's work while he was imprisoned in 1923 and he used Fischer's eugenical notions to support the ideal of a pure Aryan society