Two recent, two older.
One: "neurocognitive processes associated with self identity underlie extraordinary empathy and altruistic motivation for members of one's own social group."
Two: "participants displayed activity over motor cortex when acting and when observing ingroups act, but not when observing outgroups – an effect magnified by prejudice and for disliked groups (South-Asians, then Blacks, followed by East Asians)."
Three: "What we found was that students were more likely to choose the white confederate as a partner (63 per cent), despite the fact that the white person had made a racist comment about the black person," said Kawakami. "And the racist comments ranged from moderate to one of the most powerful anti-black slurs in the English language." (pubmed)
Four: "Blacks may, ironically, prefer to interact with highly racially biased Whites, at least in short interactions." (pdf)