Go to Dillards/Macys/Mensware House and talk to them, explain that you have a professional school interview and need something appropriate. Black is to formal in my opinion, and I went with a dark charcoal. Obviously don't do something with stripes, you want to look professional not like a pimp or your in the mafia. I personally would stay away from colored shirts as well. If you want some color use the tie to get it, just dont go over the top. Also these places will fit the suit and tailor it to you so it looks properly. Those guys do this all day long, everyday, they wont steer you wrong.
Not sure what your budget is but Mensware house will probably be the best buy.