Racism and social class are strongly confounded in America [View all]
(as well as in many other parts of the world). Race is, among other things, a sort of marker for class; thus the black professor is not recognized as belonging in an upper-middle-class neighborhood, and the cops act stupidly based on the marker (and their own pre-wired stereotypical assumptions about it).
Nobody gonna mess with Oprah, though. Unless, of course, she tries shopping in a high-class store in Paris, where her starhood is not recognized.
White folks are always willing to make a few exceptions for darker-skinned folks--Sammy Davis Jr., Cosby (at least before the fall), Tiger Woods, Oprah, as long as they have plenty of money, are clearly recognizable, and portray non-threatening and domesticated images to the Establishment.
This is not in any way meant to suggest that racial prejudice does not exist on its own, or that it is not a powerful social force, but rather, merely to describe it as part of a deeply entangled context, and to suggest that race & class are intimately linked, with racism being used as a major tool in holding down the working class of all races.
Long ago, black workers were imported into northern towns as scab labor. The white unions at first attacked them, and certainly didn't allow black membership. Then the labor leaders finally figured out that the racism was being used against them, and their only way forward was to allow black membership. Thus they had a simple financial reason to promote integration, regardless of their personal racial sentiments.
Racism still exists of course, and it is very prevalent in uneducated poor whites. But then so is anti-unionism. Both racism and anti-unionism are attitudes strongly fostered among the public at large by those who would keep the whole of the working class enslaved.