Eye color for a plausible argument stating that some eyes can or do change, based on chemical reactions and hormonal changes within the body. Studies on Caucasian twins, both fraternal and identical, have shown that eye color over time can be subject to change, and major demelanization of the iris may also be genetically determined. Most eye-color changes have been observed or reported in the Caucasian population with hazel and amber eyes. Carleton Coon created a chart by the original Martin scale. The numbering is reversed on the scale below in the (later) Martin–Schultz scale, which is (still) used in physical anthropology.
Adams chromatic valence color space what Hunter used in his Lab color space. As with chromatic value, these functions are plotted with a scale factor of 2⅛ to give nearly equal radial distance for equal changes in Munsell chroma. Adams' color spaces rely on the Munsell value for lightness. Defining chromatic valence components formula_22 and formula_23, we can determine the difference between two colors as: where V is the Newhall-Nickerson-Judd value function and the 0.4 factor is incorporated to better make differences in W and W perceptually correspond to one another. In chromatic value color spaces, the chromaticity components are formula_25 and formula_26. The difference