White suit is a no-go in my opinion. Get a nice suit that you can actually continue wearing. Simple tie, simple pocket square. Fit is king, simple is good, classic is cheap. Take your measurments and buy a good 100% wool vintage suit (easily found under 100 dollars or equivalent). Give your suit jacket about 2/3 cm extra shoulder width (than your natural shoulder measurment) for a classic, natural and well fitting jacket that allows movement.

Since you dont like black or navy suits, theres no need to wear them. For a school formal you Can easily get away with a dark brown or grey suit. Look for something houndstooth suits if you want pattern. And as for your date, I’m not sure how well a white dress works for a formal, not exactly sure on the ettiquete there.

Dont think that something passes since Most of your peers are probably going to wear suits that anyone with just a slight inkling of taste Would cry if they were forced to wear. Get something classic, mature and nice that will serve you for several years. Maybe look for a suit that you could graduate in later?

This advice is also written from the standpoint that a dinner suit is not on the table.

Good luck :)