Which three highest-selling authors — counting both during their lives and after — were at least partly black? Naturally, the definitions, both of best-selling and partly black, are necessarily vague. But I'm looking for people at least some of whose relatively recent ancestors were of the racial groups that we generally call "black," and that were known by many others and by themselves to be at least partly black. (My sense is that this is the normal American usage of the term; whether it's a good definition or not, that's the one I'm using here.)
For best-selling, I've looked at all the people noted throughout this Wikipedia page, though I'd certainly accept rival claims. I've deliberated focused on best-selling status to try to keep things as objective as possible, though naturally one can point to authors who were great and even successful who don't make this list for a variety of reasons). My view is that two of the people I have in mind have legitimate and broadly acknowledged claims to literary greatness and not just popularity, but that's of course subjective, as is the question whether their greatness materially exceeds that of, say, Maya Angelou or Wole Soyinka or many other candidates.
UPDATE: I originally just asked for "best-selling," but I meant to ask for the three highest-selling -- I don't just want popular authors, but extraordinarily popular ones. I corrected the post accordingly.