Wow, so much back-and-forth about something that should be obvious. The folowilng is just my opinion on what I've seen in my time and what I would hope to see. This one of the single most important events of your life. This is not a time to be against-the-norm or a time to "be yourself". When you go on a professional interview (which is exactly what this is), the clothes need to be invisible. Thus,you need to dress, as they say, to the nines. When you inteview for a position, you dress for the next highest position. This is a medical school spot you're vying for, not a managerial job at Taco Bell. Try a suit (blue or grey, but definitely not black, this isn't a funeral), with no other color than a white shirt (colored shirts are for second, more casual interviews), dress shoes, a tie that offsets, yet balances the color of your suit (and please, use a tie tack). Hair should be neatly cut and combed and for men, this is the best time to remove any and all piercings (except the ones, they can't see of course). Women, should of course follow similar dress patterns. A mid-calf skirt suit is always lovely. I'd pass on the high heels as you'll be walking around most of the day. Wear one earring in each ear, and no nose rings. One girl at one of my interviews wore a nose ring. That would be an outstanding spot for the interviewer to focus attention.
I understand in undergrad there is a strong sense of indivduality as you find yourself and who you're going to be. My advice is to just to suppress it for the interview.
Andrew