<P> In humans , the pigmentation of the iris varies from light brown to black , depending on the concentration of melanin in the iris pigment epithelium ( located on the back of the iris ) , the melanin content within the iris stroma ( located at the front of the iris ) , and the cellular density of the stroma . The appearance of blue and green , as well as hazel eyes , results from the Tyndall scattering of light in the stroma , a phenomenon similar to that which accounts for the blueness of the sky called Rayleigh scattering . Neither blue nor green pigments are ever present in the human iris or ocular fluid . Eye color is thus an instance of structural color and varies depending on the lighting conditions , especially for lighter - colored eyes . </P>
<P> In humans , the pigmentation of the iris varies from light brown to black , depending on the concentration of melanin in the iris pigment epithelium ( located on the back of the iris ) , the melanin content within the iris stroma ( located at the front of the iris ) , and the cellular density of the stroma . The appearance of blue and green , as well as hazel eyes , results from the Tyndall scattering of light in the stroma , a phenomenon similar to that which accounts for the blueness of the sky called Rayleigh scattering . Neither blue nor green pigments are ever present in the human iris or ocular fluid . Eye color is thus an instance of structural color and varies depending on the lighting conditions , especially for lighter - colored eyes . </P>
where do blue and green eyes come from
where do blue and green eyes come from
Tyndall scattering of light in the stroma
Tyndall scattering of light in the stroma