I proposed rolling the gender randomly when you create NPCs. You could extend that to race and preference if you wanted.
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Personally, I see the same challenge trying to incorporate black NPCs into the game. With the D&D races, I just make them come from different places (like their real world counterparts). So saying where black people come from isn't as obvious to me, because other than "from a place like Africa", which i don't tend to put in my euro-medieval worlds, kinda makes it hard.
When I had a bunch of wererats attacking a crowd at the fair, I had their victims descriptions totally randomly determined -- gender, age, social class, occupation, and D&D race (e.g., Halfling). I didn't bother describing sexual orientation or races within humans as it didn't seem relevant. I do that sort of thing whenever I need to make up NPC's on the spot.
The chances though, are not all even. For example, for a night watch patrolman, I might say 1-7 human, 8 dwarf, 9 half-orc, 10 other race (infravision is valued), and gender 1-7 male. Whereas a daytime watch patrol might be 1-7 human, 8 elf, 9 half-elf, 10 other race.
As for races of humans in my Greyhawk campaign, I think of it like this, and combining somewhat unrelated Earth origins (Greek & Mongol within Baklunish), I can give it a lot of historical and cultural flavor while not having it exactly like any real culture.
-- Suloise = northern European. English, Scandinavian, and Finnish. I even give them Norse gods + Suel specific gods.
-- Oeridian = southern and central European. Italian, French, Celtic, and German (Holy Roman Empire = Great Kingdom). I give them "default" Greyhawk gods, most of which are Oeridian in origin.
-- Flannae = original people of the Flanaess = Native American/First Nations, with weird admixtures of Sumerian and Swiss (as Perrenland is theirs). I give them American Indian gods (from AD&D Legends & Lore), Sumerian gods, and specific Flannae gods.
-- Baklunish = "eastern" people = Greek, Turkish, Hungarian, Middle Eastern, Mongol, and Russian. I give them Greek gods, plus specific Baklunish gods.
-- Touv = subSaharan African = We've never been to Hepmonaland, so their gods are unknown. They show up as a subsection of the population on the coasts of the Azure Sea -- Cauldron, Sasserine, Holds of the Sea Princes, Keoland, Wild Coast, and Greyhawk City. They came as merchants long ago, so they tend to be rich, but rare. They follow "normal" Greyhawk gods (mix of mostly Oeridian, some from the other races).
-- Olman = Central American natives = We're never been to their homeland, so we don't know their gods. Extremely rare outside their homeland, except in the Hold of the Sea Princes and Cauldron/Sasserine.