I gotta say that I'm amazed people still ask these types of questions. This is an interview for professional school.
Men: Well tailored suit (it can be slacks, shirt and tie and a nice blazer, but suit preferred), nice shirt and tie, nice dress shoes (not DCS/Vans of matching colors with your suit), well groomed hair and facial hair (or lack thereof...not in between).
Women: Pant suit or skirt suit (of appropriate length, no mini skirts pls), nylons (if in a skirt) and neutral blouse (no crazy colors or patterns), reasonable shoes (no crazy stiletto heels or odd styles/patterns), purse (?).
An interview like this is not necessarily the time to assert your individuality or spite your parents with the goth look.
Yes, you need to somewhat look like every other applicant. Wow them with your personality and knowledge, not with the pink and purple polka dotted shirt and Captain America tie.
Leave the cell phone at home/in the car/at the hotel.
When you are the interviewer, you'd be surprised how when someone dresses oddly, you don't even hear what the applicant says. All you think is, "I can't believe this person actually showed up dressed like that". Also, this may seem shallow, but if you show up in a $2000 suit/outfit, it can be a bit off putting. Be reasonable.
Is that the first impression you want to give?
Btw this also transfers over to when it's time to visit/interview with residencies.