There's black in all of us?

Chris Rock is the funniest guy on earth. I love all his movies (that I've seen so far). One of my favourites is Down to Earh . His character Lance is a budding comedian who is hit by a bus and dies before his time. Wishing to return to earth, but unable to inhabit his former body, he is placed in the corpse of a rich, white Manhattan mogul. Living in the body of a callous old white man would be bizarre enough for Lance without falling in love with Sontee, the beautiful woman publicly battling Wellington's company at the same time. And as if that wasn't enough, he's got to deal with the love affair between Wellington's wife and his personal assistant, and their plot to have him killed.

This theme of black people impersonating white people (such as White Chicks) or in the case of Down to Earth, trapped in a white man's body - making fun of white people is always funny. Its ok? But would it have the same effect the other way round? I think its funny if the black man makes jokes about race, but just plain racism if a white man does it?