I would say that almost anything goes, but the "no goes" are very important. For example, bright, primary red with navy will always have, to my eye, a "grand old flag" look, whereas a wine red would be just fine. True white would have the same effect as bright red.

I would probably also not do something like cobalt, which could look like you tried to match and failed. (If matching is what a person is going for, I feel it should MATCH. If it isn't, it shouldn't look like it was trying to.)