Green has traditionally been called the rarest eye color. But new classifications say another color may be even less common—gray.Eye color is an inherited trait with multiple genes affecting the shade. Genes related to the production of pigments—melanin, eumelanin, and pheomelanin—dictate the color of your skin, hair, and eyes. A person's eye color reflects a unique combination and concentration of pigments in the iris.
Source: Verywell Health