I don't remember them in the books, but I'm sure you know what you're talking about. I guess, when I read books, I don't notice what ethnicity the people are. To me, it just seemed to be a little too PC to be adding minorities just for the sake of appealing to the new immigrants to Britain. Not that I see any problem with it; it was just unexpected for someone who doesn't pay that much attention to such details. Come to think of it, there's a lot of different countries that pop up in the book, including Cho and some Russians from another school.
Dean Thomas (Harry's Dorm mate) is black, as is Lee Jordan, the twins' buddy in mischief.