What you call "white" and "black" people are actually neither black nor white; rather, they differ in the darkness of the red component of their skin color. (Though most don't view brown as red, its color breakdown is dominated by red; some cultures do see brown as a type of red.)

This actually ties in with why clippys don't visit earth. To put it bluntly, "These beings terminate each other over relative skin redness. I'm silver. Exit!"