The Legion of Super-Heroes was surprisingly slow to integrate, considering the millennium that had passed between the modern day and the world of the future; sure they boasted a green-skinned and an orange-skinned member from the start, plus the blue-skinned Shadow Lass later on, but to paraphrase Green Lantern’s great foe The Old Black Scold Who Wandered Up To Him On The Street One Day In That Denny O’Neil Comic: “What about the black skins?”
It seems unlikely that the 30th century would be populated entirely by white people, particularly as they currently only comprise, using that Global Village of 100 model, about thirty percent of the world population. Of course, the issue was that It Was A Different Time™ and even those members of the earlier Legion which had reportedly been originally envisioned as non-white – Karate Kid and Ferro Lad, specifically – were whitewashed.
It wasn’t until the Seventies and Eighties before the question of where all the different ethnic groups had gone was uncomfortably answered – um, they fled to their own planets and dimensions. Well, could you blame them? Representing North America’s indigenous populations, Dawnstar’s people colonized a distant world (and grew wings) while Tyroc’s people (descendants of the African slave trade) disappeared into an other-dimensional island which spirited away every two-hundred years (and which paralleled European social and cultural evolution in the interim … looks like someone with otherwise best intentions accidentally pressed the Oops! All Colonialism! button over at the DC offices).