It seems odd that NBC would have no issue with a dark-skin man/light-skin woman romance (Space Seed) but would have an issue with a light-skin man/dark-skin woman romance (The Alternative Factor).
Or did NBC have issues with the Khan/McGivers romance?
They (the network, people, whatever) had issues with black/white, not "dark/light." Cuban Desi and "Whiter and White" Lucy were married and parents for years before Star Trek. When they talk about the first interracial kiss, they're not thinking about Montalban and Rhue. It wasn't "dark skinned" people who were being singled out. It was blacks.