Trek alien races

[Eonwe]

I know this has probably been done many times before, but I was watching The Undiscovered Country a few days ago, and thought that, well, no wonder Klingons and Romulans always are looking to fight other races. They clearly never had to deal with living amicably with folks who look different than they do back home, because they have zero racial diversity whatsoever.

At camp Khitomer we had numerous varieties of human, while all the klingons looked exactly the same.

Again, I know this is old hat, but the weird irony just struck me. Is there any 'canon' material that adequately deals with this bizarre issue?

(and, for the record, I understand the logistical reasons for doing it on the show. And, look how long it took to get a 'diverse' vulcan. And even then, Tuvok looks like a human of African decent with pointy ears. If Vulcan is a desert planet, and most everyone has pale skin, under what conditions did dark-skinned, large-nostrilled Vulcans live?)