This is a very interesting question. There was a bizarre degree of outrage when some of the halfling art for 4e showed halflings with braids, cornrows etc (see eg p 44 of the PHB).
There's also the wierdness that the AD&D monster manual describes dwarves and gnomes as typically dark-skinned, yet in D&D art they are almost always white (often with red cheeks). Here are the OSRIC descriptions, for example (pp 192-93), which are very close paraphrases of the AD&D MM:
Dwarfs have a dark brown to deep tan coloured skin tone.
Gnomes have wood brown skin
Gnomes have wood brown skin
But I don't know that I've ever seen a picture of a dark-skinned dwarf or gnome in D&D art, from the AD&D period or more recently.
The 4e PHB says of dwarves that "[they] have the same variety of skin, eye, and hair colors as humans" and gives us two very pale dwarves (pp 36-37). More oddly, the PHB2 says of gnomes that "[their] skin tone ranges from a ruddy tan through woody brown to rocky gray" while giving us a picture of a very pale gnome and another whose skin tone is a bit ambiguous but is probably olive-skinned (pp 10-11). The gnomes on page 134 of the MM and p 129 of the MM2 are also pretty pale - no ruddy tans, let alone woody browns.
Eladrin are said on p 39 of the PHB to "have the same range of complexions as humans, though they are more often fair than dark." The art certainly emphasises the tendency towards fairness. Elves, on the other hand, are said on p 41 to "have the same range of complexions as humans, tending more toward tan or brown hues." I challenge anyone to find a brown or even tanned elf in the 4e art! Those on p 40 of the PHB and p 106 of the MM are quite pale, especially in the latter case.
Tiefling skin colour also "covers the whole human range", according to PHB p 49, but the art on p 48 and on p 250 of the MM does not reflect this.
Make of all that what you will.
