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.
Natural Color System lightness value "v" as the sample on the reference scale to which it has the least noticeable edge-to-edge difference. Two examples of NCS color notation—the yellow and blue shades of the Swedish flag: The NCS is represented in nineteen countries and is the reference norm for color designation in Sweden (since 1979), Norway (since 1984), Spain (since 1994) and South Africa (since 2004). It is also one of the standards used by the International Colour Authority, a leading publisher of color trend forecasts for the interior design and textile markets. In order to be able to manufacture physical representations of