Eye color is a polygenic phenotypic character determined by 2 distinct factors: the pigmentation of the eye's iris and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris. Babies, who have European ancestry, their eyes color will change when the grow up. Because when they grow up, melanocytes begin to produce melanin, and melanocyte cells continually produce pigment to change eye color. Eye color will also change during puberty, pregnancy and after serious trauma as a result of chemical reactions and hormonal changes within the body. So normally, if you are an adult, it's not possible for you to get yellow eyes naturally, or you may get sick if you get yellow eyes suddenly. But you can wear yellow colored contact lenses to get yellow eyes.