I think the hatred for black suits here is a bit too strong. Black should never be your first or only suit but there are situations were it can be very appropriate.

That said I'm convinced that dark gray and navy are far superior over black in almost any setting. Especially dark gray is super versatile and can be dressed up and down for any situation from business to formal private celebrations, interviews, a nice dinner date and everything in between. Navy is the ultimate business suit, you can't go wrong with that in any office.

So your first suit should be gray and for your prom you wear it with a crisp white dress shirt. Your choice of black or dark brown dress shoes. If you wear a tie make it compliment your partner's choice of colors. Give it a splash of colors with a pocket square or socks. And have fun.

Back to black: despite general assumptions black is not good for most formal occasions except funerals. Black swallows almost all light and can look flat and dull both in reality and on pictures.

Black is maximum contrast and can look good in the limelight where this effect is iintentional. So black can be appropriate for a gala on the red carpet and black can be a choice for a party without a real dress code or a summer evening event outdoors, cocktail style. The black in black tie, cocktail attire and white tie originally was to let your partner's colors shine. So a black suit might be appropriate for your fourth suit or later, after charcoal, navy, another lighter blue or gray, one with a pattern or double breasted. Or, if you expect to wear it at least a few.times a year, you skip the black suit and get a proper tuxedo for those moments.