The characters that we *know* are black are Angelina Johnson, Dean Thomas, Lee Jordan, Kingsley and the Zabini family. In all cases we are told either that they are black or that they have dark skin, and in addition there's a drawing Rowling did of Dean which clearly shows him as black with cropped Afro hair (Lee iirc has dreadlocks). Plus we have at least two presumably Indian- or Pakistani-origin students (the Patil twins), at least one presumed Jew (Anthony Goldstein) and Cho Chang.
In addition, there are a lot of characters whose ethnicity isn't specified. If we leave aside the rare possibility of albino or red haired people of African or Asian descent, because they're statistically unlikely in such a small population. then any character who hasn't been specified as having pale skin, hair or eyes potentially *could* be black. The early films have a black Lavender, for example, and there's nothing against this in the books. All we know about Lavender's appearance is that she has a wide smile, and she can't be the absolute black you sometimes see in people from the equator, because you can tell from a distance whether she is blushing, That aside, she could be anything you like.
