Dwarves should obviously be white, since they spend almost all their time underground, where no sun reaches them.
Orcs, goblins, trolls and so on are either green, black or grey. So making them dark skinned makes no sense.
Elves... I always thought of them as pale. As if sun light is something that don't really become them. But perhaps black elves wouldn't be so strange. There are forest elves... How about rain forest elves? They could be living as one with the forest, having cute little monkeys as companions or hunting together with big cats.
Or desert elves, riding their camels, or something similar, as lone and wise wanderers of the sun burned sand dynes.
Just trying to come up with a few ideas