Though I do not dwell on it, I describe my wizard and wizardess, Im and Na, in ‘The Ways of Wizardry’ as having dark skin and curling blond hair. Genetically, they and the people of their city Hirstel are essentially aboriginal Australians. The Tesrans, whose city and nation they seek, derive from the same stock, long separated. The blond hair thing does crop up among those of that genetic background and in the isolated city of Hirstel it had become universal.
The god Xido is not exactly of any ethnicity, being, after all, a god. He, too, I described as dark or as black. As are his pantheon’s primary worshipers, Xido is more-or-less Melanesian. Or, we might better say, he looks Melanesian — when he doesn’t turn into a crocodile. Although none of his people play a role in ‘Ways,’ they are know as the Bazu and are referred to as occasional visitors (and sometime pirates).
The Ildin are vaguely Mediterranean or Mid-Eastern. I see them as having a quite varied heritage, as do most populations in their part of the world. There is some Iranian (in the broadest sense) ethnicity involved but certainly others as well. The lighter-skinned ‘Charcha’ (who later become the Sharshites of my Donzalo books) are also a mixed lot but might include Greeks among their ancestors, along with many other groups.
All this stems from the idea that all human ancestors in that world came from other planes, the bulk of them from this world of ours. There are two ‘gates’ leading from ‘here’ to ‘there,’ one in the South Pacific — through which only boats are likely to pass — and the other somewhere in the vicinity of the Ural Mountains. This latter is likely to have admitted only one or two individuals at a time, over thousands of years, so we do not have any large-scale entry of one ethnic group or another there. In the Pacific, not quite so — a boat might carry several people and the Mora are recorded as having arrived in nine large canoes. However, passage would be a lot less frequent occurrence in the middle of the ocean!
In both instances, it requires a manifestation of physical power to pry the ways open, such as a large storm. Not everyone came in that way, of course; those were just the two easiest doors to the world. Some of that is explored in the novel.
This leaves only the Dwarfs. Well, we know what dwarfs are like, right? Mine are sort of that way and sort of not. From a genetic standpoint, they are somewhat diminutive descendants of the Neanderthals. So I described them as such; we have a fairly decent idea as to Neanderthal appearance these days, thanks to having their genome sequenced. Light skinned, some of them redheads, stocky, heavy brow, and every bit as bright as other humans. Or as stupid, sometimes.
So that is it. Of course, it is a big world and there are plenty of other populations elsewhere, developing in their own ways, sometimes mixing and merging, building cultures, borrowing ideas and languages from their neighbors. Just as in our own world.