I have always gotten annoyed when the people on the covers of books didn't accurately represent the characters within. I used to wonder why authors allowed that, until I learned that they have almost no say in book covers. (I link to Jenny Crusie because I learned this through her blog, although plenty of other writers discuss this as well.) Still, I mostly thought of the inaccuracies as random, not having an overall pattern. Well, I should have known better.
For example, I recently finished Samuel Delany's Neveryona. I had stared at the cover for a while and noticed the following:
1) The man is "gigantic," but the artist depicts him as similar in height to the heroine.
2) He is wearing the wrong number of belts.
3) He's not Mr. Hygiene, but the cover has him depilated and oiled up like a Chippendale.
4) The heroine has bushy hair, but it is shown as just slightly curly.
5) She looks vaguely Italian, but she is half black and half ... well, we don't know what the predominate race is, but it explicitly neither black nor blond-white.
The wrong number of belts surely was random, but the decision to render a biracial woman as white surely wasn't, especially in the predominately white world of sci-fi. A few days later, I saw this blog post by an author about her book where the black protagonist is shown as white on the cover, which jarred me out of my naivete (ok, my white privilege). In the case of her novel, the cover has misled readers about the identity of the narrator because she is an unreliable narrator - but she isn't wrong about her race. In the Delany case, by contrast, the reader has no cause to doubt the narrator, general postmoderism aside. But both covers represent a systemic tendency to "whitewash" covers; try finding a book with a white protagonist depicted as black.