I don't think there are any rules that work any more - I try instead to think in terms of appropriate.

Beach wear for the beach! Hunting clothes to hunt in. Ski wear for sliding down the slopes. etc, etc, etc...

Appropriate clothes to fit the event.

A few years ago, no one would have thought that a black shirt would look nice with formal attire. But we have seen several members that manage to make it look very nice.

Just remember the golden question: "Honey, does this fill in the blank make me look fat?"