...or, you know, maybe skin color has nothing to do with climate in your game. There's no reason it should have to.
[tangent]Elven pigmentation since 1st edition has been backwards of human pigmentations.
The grey elves that live on high mountain tops under the harsh sun are bone white in skin and have light colored hair and eyes.
The 'high' elves that live among men, more or less, are the same coloration as men.
The wood or wild elves or grugach are described as darker, or 'nut-brown.'
The dark elves who live underground and never see the light of the sun are dark, dark, dark.
The aquatic elves, who live in the blue-green waters are blue or green.
Humans would get dark in the sun or pale in the underdark, but D&D elves bleach in sunlight and darken in shadow, it seems.
If there were elves living on the elemental plane of fire, I'd expect them to be red-skinned, to match their surroundings.[/tangent]
.
At the end of the day, I don't care whether or not it makes sense to have black, brown, yellow, red, etc. humans in the setting. If putting one on a cover helps to expand the market (and the number of people I can sit down and game with), then, do it. A larger customer-base is good for the business, and more players is good for all of us. Nobody needs to bend over backwards to make me feel included with pictures of more white dudes, 'cause I've never felt
excluded.
As for the presence of non-whites in a fantasy setting, I liked Kingdoms of Kalamar, for making their Svimovish or whatever a peer-equal culture and kingdom, with it's own advanced crafts, bustling metropoli and magical academies and whatnot, and not the primitive jungle savages tucked out of the way that other settings have tended to reduce their black presence to.