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
Forel-Ule scale sea and lake water colors, as they appear to an observer ashore or on board a vessel. The method is used in conjunction with the Secchi disk submersed to half the Secchi depth. The method was developed by François-Alphonse Forel and was three years later extended with greenish brown to cola brown colors by the German limnologist Willi Ule. The Forel Ule scale, a color comparator scale, has been described by Wernand and van der Woerd (M. R. Wernand, H. J. van der Woerd, "Spectral analysis of the Forel-Ule Ocean colour comparator scale.", J. Europ. Opt. Soc. Rap. Public. 10014s