Yes, there is a prominent black student, Lee Jordan, who among other things announces the Quidditch matches, and is the Weasley Twins' best friend. There are characters like Parvati Patil, whose race is not discussed but who must be south Asian. (Parvati, by the way, is described as the most beautiful girl in Harry's year, and has a twin sister, Padma, in another Hogwarts house). There is one senior wizard who is West Indian in the Order of the Phoenix, and Cho Chang who is Asian. Not a huge number of folks, but it IS set in England, so McGrath is probably right--about what you'd expect, especially since the vast majority of students and wizards are people we don't know anything about, including their race.

Both the people Harry has gone on dates with, BTW, are Asian: Parvati and Cho.

I think what Rowling is doing with the race issue is subtle. She has created a wizarding world in which nobody cares what "race" you are--it just doesn't come up. (No one says that Parvati and Padma are Indian, and Lee's blackness is mentioned just once, I believe.) Instead, whether you come from a good old wizarding family, or are instead a "muggle-born" or "mudblood." is the relevant quality. She has eliminated ordinary racism and race-consciousness on purpose, I think, to highlight the fact that prejudice against muggle-born wizards is the wizard version of racism. Then she is pretty relentless about making sympathetic characters like Hermione muggle-born, sympathetic characters like the Weasleys muggle-loving, and unsympathetic characters like the Malfoys muggle-hating (and "mudblood"-hating, too). Occasionally, a good person will make a generalization about muggles, and you automatically feel that inner cringe of guilt. I think it's pretty well managed, actually.

Blackcatter, you are right, it's good to discuss issues like this!