Start with a classic dark suit, in navy or black — plain is preferable.
Depending on your shirt and tie, it’s as good for business as it is for semi-formal functions.
 
Your second suit should be something in a dark gray. It’s a smidgen less formal, but useful just the same. Don’t be afraid of pattern.

Suit number three should be black or navy, whichever you did not opt for in step one, with a different pattern or texture from your first two suits.

Try something with a stronger pattern for your fourth suit. Have fun.
Express yourself.