A substance called melanin determines eye
color. If an eye has a lot of melanin and the melanin is near the surface of
the iris, then that eye will be a darker color. An eye with less melanin
farther from the surface will be a lighter color. How much melanin we have is
inherited from our parents. Melanin protects our eyes from absorbing strong
light, that is why, generally speaking, a blue eye is more sensitive to bright
lights than a dark brown eyed person.