I wouldn't say that black metal is for white people. But for some reason, mostly white people like black metal, or metal in general. Some Asians and latinos are into metal, but for some reason very few blacks are into metal. I think that most blacks see metal as "white man's music," and since most of them hate white people, they don't want to listen to it. Also, Africa by far has the smallest metal scene (ignoring the South African scene, which is all white). There are a couple bands from Angola and Botswana, but that's it.