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 regime, Fischer developed the physiological specifications used to determine racial origins and developed the so-called Fischer–Saller scale. He and his team experimented on Gypsies and African-Germans, taking blood and measuring skulls to find scientific validation for his theories. Efforts to return the Namibian skulls taken by Fischer were started with an investigation by the University of Freiburg in 2011 and completed with the return of the skulls in March 2014. In 1944 Fischer intervened in an attempt to get his friend Martin Heidegger released from service in the "Volkssturm" militia. However, Heidegger had already been released from service when Fischer's