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
Shades of green 2005 it formalized the colors which it would use. The color "screamin' green" is shown at right. This color was renamed from "ultra green" by Crayola in 1990. This color is a fluorescent color. "Sea green" is a color that resembles the sea floor as seen from the surface. "SGBUS green" is the color voted by the public and used by Singapore to colour all its government-owned public buses. "Spanish green" is the color that is called ""verde"" (the Spanish word for "green") in the "Guía de coloraciones" ("Guide to colorations") by Rosa Gallego and Juan Carlos Sanz, a color