The eyes colors, and specially the iris colors, are regarded by many scientists as of no importance to the visual functions of the eye. I think there are good physical reasons to the iris colors, as well as to any color in animal and plant. In the pages of this site regarding the new theory, BioColorPhysics, we see a Table which gives a one-to-one correspondence between the Colors and between the Mechanical and Thermal physical properties. Using that Table I find reasonable physical explanations to the eye colors of many animals. I emphasize mainly the human iris colors.

Eye colors are determined mainly by the structures of the iris. Iris structure should be in accordance with the main function of the iris. The iris functions as a variable diaphragm in front of the lens. The iris dilates or constricts the pupil, so that only appropriate amounts of light may reach the lens. Contraction of the radial smooth muscles of the iris dilates the pupil. Contraction of the circular smooth muscles around the pupil constrict the pupil. There are several techniques for contracting the radial smooth muscles. Two of them are: Torsion and Shrinking. According to that Table of BioColorPhysics, the Bluish color in the eye hints about using mostly the Torsion technique, while the Brown color hints about using mostly the Shrinking technique. Brown color includes Black color. There are many Black color patches in the iris. These are due to Black Melanocytes. According to that Table, Black color hint about the need for Tension Stiffness at the places where they appear. Indeed, when looking at ultrastructures pictures of the Human iris, Scanned by Electron Microscopes, one finds simple Mechanical explanations to those Black patches. Using that Table, one may find Mechanical and Thermal properties of each colored patch in the iris of any Human's or Animal's eye. I am preparing now (October 2002)  a big  article about this subject. If you wish to see a draft of my article, please e-mail to me via the CONTACT button at the top of this page, or fill up the Form for Articles Order.