Look around you in America today at the various shades of skin color, from transluscent white to pitch-black and everything in between. Skin color gets more easily mixed than eye color.
Two blacks marry, their child will be black. Two green-eyed people married, and you have no idea what color the children's eyes will be.
A white and a black marry, and the child will be black.
Next question?
Classification of people into race based on morphological characteristics is right and proper science. Treating humans differently because of those classifications is racism. Don't confuse the two.