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
Gardner color scale the liquid. This procedure isn't extremely accurate due to variations of observers, illumination and to some extent the standards themselves. Gardner Color can also be measured by a dual beam xenon flash spectrophotometer, for example the ColorQuest XT. Spectrophotometers measure the percent transmittance of the product and automatically calculate and provide the Gardner color number using illuminant C and 2º observer. Gardner color scale Gardner Color Scale is a one-dimensional scale to measure the shade of the color yellow. Colors of transparent liquids have been studied visually since the early 19th century. Changes in color can indicate contamination or impurities