A black suit is good for formal use. Church-business, meetings with executives etc. You're conveying the message that you're dead-serious. A charcoal suit works well, also, as mentioned in another comment.
A lighter suit, maybe grey with a very light pattern, no color, goes well for anything non-dead-serious. The message is that you respect and take whomever you're with seriously. Lower level meetings, fancy restaurants, conferences. A black suit don't go well here, because the situation just isn't dead serious.
The third suit is for when you're used to wearing suits and like it (if you don't like it, don't go there) - something more playful, something like a color pin-stripe is popular. Generally not for business-use, but for going out. If you show up at a post-conference cocktail reception in a suit like that it says "let's enjoy ourselves" and shows another side of you.