Don't know if this counts for anything(since the authors here are white), but it seems like covers tend to get white-washed a lot even when the character is explicitly described as being black...Examples.
^ Described as dark skin and nappy, had to go through different covers before the author had to take the middle ground and settle for the mixed girl.
^ Set in Africa.
Set in Africa, described with dark skin.
^ Black chick.

^ Described as dark skin and nappy, had to go through different covers before the author had to take the middle ground and settle for the mixed girl.

^ Set in Africa.

Set in Africa, described with dark skin.

^ Black chick.