Let me see, in a virtual world you are by definition incognito. You can present a face to the world that is not the one you would present in face-to-face public situations.
So I think it is hardly news that racists would be even more racist online.
The funny thing is that there are probably loads of people who adopt avatars of a different skin color than there own - and they get buzzed the same (and probably do it too !).