No rule is inviolate
I never played in Dark Sun, but just assumed that demi humans there were ethnic due to the climate. A quick google search reveals that's not the case, and they're almost all white. That's....disappointing and a miss from the TSR team when creating Dark Sun, and WoTC when continuing it.
I did and still do. The 1990s art was simply a reflection of expectation of what sold to a typical D&D gamer at the time, even though the setting itself was neutral on whether it could be inspired by European, African, Asian, or some other real-life area. And, at the time, it sold big. You'd have to search a bit to find non-white European art in D&D at any point prior much less any artistic depictions of females who weren't big-breasted, athletic, and scantily clad. So, I wouldn't label it a Dark Sun miss. The books didn't say one way or another, even if the artists did. A generation later, target audiences have diversified, and I expect if released again the art would catch up.