Makeup is part of it but there are plenty of other makeup-lite aliens in the Star Trek universe. Any mixture of human, betazoid, bajoran, vulcan, hardly any makeup at all.
I think it might be a sort of hypocrisy in the show that the Federation is multicultural where all cultures are equal but humans are in charge.
Maybe Eddington is right about the 'assimilation' thing.
Nah, it means the show had a budget.