I think it's been reasonably well explained so far that the reason for the lack of naturally darker skinned characters is due to anime influence. None of the characters are of a specific nationality (though some like Setsuki do have other cultural elements) and I'm fine with that.
The issue, and the reason that this discussion has come up, is that nonspecific race, try as it might, can't incorporate the appearance of both dark and light skin. It's traditionally lighter and has probably stayed that way because it caters to more groups. Nonspecific asian or european covers more bases than nonspecific afrocaribbean.
Of course, this does mean that a significant portion of the population has their natural colour pallet very much underrepresented but adding in a specific race can draw attention in an unnatural way when everyone else is or was a nonentity.
I don't think these things are quite as simple as they might appear but I will say this:
Dark skinned Setsuki looks pretty good and the skin tone definitely fits the rest of that colour pallet. Unlike Geiger who, to my eyes, looks like they just slapped a skin tone onto an otherwise white fighter.
More of the former and less of the latter would be cool with me but it's hard to pin down exactly what makes that difference and, if the first post is anything to go by, it's quite subjective.
I honestly wouldn't mind that being Setsuki's default costume, even, were the rest of the cast of clearly varied ethnicity enough that it wouldn't feel out of place.