Eye colour is determined by two distinct factors – the pigmentation of the iris of the eyes and the scattering of light by the front fibro-vascular layer called “stroma” of the iris. The pigmentation of the iris varies from light brown to black, depending on the amount of pigment called melanin within the stroma of the iris. It usually varies in quantity. Neither blue nor green pigments are ever present in the human iris.
The appearance of blue and green, as well as light brown colour called ‘hazel eyes’ is an optical phenomenon resulting from the elastic scattering of light by particles scattering light. It is this same phenomenon that accounts for the blueness of the sky.
It could, therefore, be said that the darker the iris, the more melanin it contains and the more unlikely it is to appear blue. Black people generally have a lot of melanin in their skin and iris in sharp contrast to white people. A person’s “eye colour” is actually the colour of one’s iris, the cornea being transparent and the white sclera entirely outside the area of interest.
Source: Nigerian Tribune