What determines the color of the iris?

genetics and the way the mothers and father genes match up.

What determines the color of the iris?
I believe it has to do with the recessive and the prominent genes.
Reply:Eye color is determined primarily by the concentration and distribution of melanin pigment on the iris fibers. The iris is located inside the eye, between the cornea (front most surface) and the internal crystalline lens. The hole in the middle is called the pupil and it changes size to regulate the amount of light entering the eye. If the iris contains pigment on both the front and back surface, the incident light that reflects off the iris is brown. Sometimes there is little or no pigment on the front surface. The light interacts with the gray iris fibers and the iris stromal cells and reflects as blue. The size and spacing of the fibers and stromal cells determines the "blueness" or "greenness' of the reflected light. Although the majority of irises have similar pigment density on the back surface (called the iris pigment epithelium), some people have less and that allows for some reflection from the retina in the back of the eye. The retina reflects red from the network of blood vessels contained within its structure. This is also what causes the red reflex in the iris pupil seen in photographs taken with a flash. The red color interacts with the blues and browns to create aqua and violet iris colors. There's a rare genetic condition called albinism in which those individuals do not have pigment on the back of the iris and their iris color appears pink. Sometimes, the pigment from the back surface “rolls” up onto the front surface right at the pupil border. This results in a brown ring around the pupil, which can look quite unusual in an otherwise “blue” eye.
Reply:The light. It's spectrum generates "colors" which are in fact different frequencies of the light wave.
Reply:a protein called melanin (which also determines skintone) - the more melanin a person has, the darker the eye and skin color will be. A person with little or no melanin will have blue eyes. This protein takes several months to develop, and that's why all babies are born initially with blue eyes.