Yo, sexual attraction, whether influenced by race, size, hair color or any other feature, is biased by nature. That's not to say that you can't pile more blatantly ignorant biases on top of those which are more instinctual but preferring someone of your own race is not racist in and of itself. There was a time (as a child) when I did not find black girls attractive. I had no context to associate their unique features with such primal feelings. However, I agree that any adult in a diverse society that exclusively dates a particular race, whether their own or not, should be held in suspicion. Unless it is a fetish I can imagine no other acceptable reason.
P.S. Yo, why wasn't this topic already posted by the Admin?