Eye color

Eye color is a polygenic trait and is determined mainly by the amount and type of pigments present in the eye's iris. Humans and animals have many phenotypic variations in eye color. In humans, these variations in color are credited to varying ratios of eumelanin produced by melanocytes in the iris.The brightly colored eyes of many bird species are mostly determined by other pigments, such as pteridines, purines, and carotenoids.
Three main elements within the iris add to its color: the melanin content of the iris pigment epithelium, the melanin content within the iris stroma, and the cellular density of the iris stroma.In eyes of all colors, the iris pigment epithelium contains the black pigment, eumelanin.Color variations among different irises are normally attributed to the melanin content within the iris stroma.The density of cells within the stroma affects how much light is absorbed by the underlying pigment epithelium.