One study looked at self-reported information about beliefs and voting patterns from Republican and Democrats, along with psychological tests measuring implicit stereotypes. "That study found that supporters of President Bush and other conservatives had stronger self-admitted and implicit biases against blacks than liberals did."
While it would be easy to jump ahead and say that Republicans are all bigots, I don't think that's true, nor does the data suggest that. In fact, another study confirms that there's much more racial bias out there than we care to admit, and it goes across the political spectrum. Another study administered a psychological test that measured associations of positive and negative attributes to black and white faces to a group of 130,000 whites. The study found that regardless of whether they labeled themselves liberal of conservative, a substantial majority had a more difficult time associating black faces with positive concepts, evidence of implicit bias. That disturbing bit of bipartisanship aside, "districts that registered higher levels of bias systematically produced more votes for Bush."
As I mentioned, this isn't really news, in the sense that the reality of racial bias in politics has a long and ignoble history. Still, its nice to have research to back up what we've known for a while.