I haven't seen the lighter-skinned Redguards, so I will have to check that when I get back in game. I agree that it's unfortunate, but I'm basing my info on the previous lore. I know Bretons can be quite tanned, but definitely not African American, if that's the specific dark-complexion that's being requested. Nords are, as someone mentioned, seemingly based on the Nordic peoples, and thus their lack of dark-skinned complexions is sensible. You also couldn't do dark hair for Nords in some games, if memory serves, because their hair is supposed to be light.
(I concur with the female vs male issue, but I'd rather not discuss it here, as it detracts from the issue at hand. It's not fair to detract from one issue by bringing up another. They are both problematic.)