Lanefan
Victoria Rules
Makes sense for Kobolds at least - most versions of them I've ever seen have them as somewhat reptilian, thus snake-like skin (green or brown and somewhat scaly) similar to that of Lizardpeople or Troglodytes isn't a big stretch here. As for the others: Orcs' skin tends to also be greenish and-or brownish in most representations, Goblins do tend to be dark, and I've never really thought about "standard" Hobgoblins as mine are very, very different to anything the original game ever had in mind.Orcs are non-white. Looking at the Lord of the Ring movies as mentioned above, the good races are consistently portrayed as white; looking at the 2ed Monstrous Manual (the first color Monster Manual), with the exception of a couple gnomes who look sort of Asian, and a one light brown human of several humans, all the PC races are white. For better or worse, most of the giants and most of the other human-like or part human creatures are also white (at least in their human parts). But orcs, kobolds, hobgoblins and goblins are all darker.

In real life, no; but in the more simplistic "heroic" game setting it's just another not-so-subtle way of hammering home the idea that evil is bad/repulsive/etc.Ugly versus beautiful may be complex racially, but it's not any less problematic to say that ugly people are evil and good people are pretty.
Lan-"beauty is in the eye of the beholder only until the beholder eats it"-efan