This would be less of an issue if the original game hadn't been so obtuse on who actually came along in the sleeper ships. It'd not be too far a stretch to imagine that the American sleeper also contained, apart from white Americans; the native Americans, the millions of their contemporary immigrants from all over the world, the list goes on.
Unless all the factions in Sol practiced some kind of extreme ethnic segregation, where no-one was allowed to leave their country of origin or have kids with someone of a different ethnic background, it'd be fair to assume that all the sleeper ships carried a fairly ethnically diverse group of people, from all over the planet, and that over time, they sort of congregated around others with similar backgrounds, forming the factions and nations we see today. Going by this assumption, it'd be fair to say that roleplaying someone of just about any ethnicity would be perfectly valid, although I'd expect that they'd be treated differently than, say, the "natives". I mean, it's not unreasonable to think, is it?