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
Linguistic relativity and the color naming debate frequencies corresponding to different colors. The lengths of habituation were measured and found to be longer when the infant was presented with successive hues surrounding a certain focal color than with successive focal colors. This pattern of response is what is expected when the infants are distinguishing between the focal colors, but not distinguishing between successive hues (i.e. different shades of red are all "red" but "blue" and "red" focal colors are different). This is to say that infants respond to different hues of color in much the same way as adults do, demonstrating the presence of color vision at