I think "reverse racism" is at least mostly, if not entirely, a made-up concept in the white-black case. The idea that some resources are limited, and if "they" get more, then "we" get less. So if a white person gets fired (maybe for good reason), and they hire a black person in his case, how convenient to tell his buddies "they got rid of me to hire a black guy," rather than "I was drunk/insubordinate/etc."

Or just feeling terribly threatened that "they" will be moving in, and, like Urban Legends, you know someone who knows someone who didn't get into law school or get a job, and in the story, it's very clear it was to let someone black in.