This is likely not surprising to evolutionary biologists/psychologists, but studies would seem to indicate that a preference for one "race" (used loosely, because many scientists disparage the use of that term as being technically inaccurate) is either in-born or learned very early in life depending on the predominant race one grows up around.
An article on the study can be found here.
The reason this shouldn't be surprising is that humans have a great many evolved traits that served us well when we were scrambling to stay alive a few million years ago in the African savannah, but are counterproductive for the industrialized, high-tech, urban lives many of us lead today.
When we lived in Stone Age tribes of 100, an innate fear of anyone who didn't look like the people we grew up with might easily save our lives when another tribe ambushed ours to take over the local water supply. Our instinct to defensiveness, the numerous ways that emotion overcomes reason, and so many of our fears helped us survive in the past, but complicate and contradict each other now. It's likely that at least some part of racism is similarly rooted.
But as with other remnants of our past which no longer fit, that doesn't mean we just accept them. We no longer allow for unchecked emotion to be a legitimate excuse for committing crimes against others, we expect people to restrain themselves. Regardless of our predispositions, racism belongs in the same category. The main impact of these findings is simply to make the problem easier to understand.