アザ？

Many Japanese people say, "I have black eyes."

A black eye is what happens when someone punches you in the eye. In a fight. Most Japanese people have brown eyes- light brown or dark brown. My eyes are blue. My mother's eyes are green. But humans don't have "black" eyes. So if you say "I have black eyes," it's strange. 

In English, most Japanese eyes are brown. ^-^