sitting in on interview

Your clothing should be the least noticeable thing about you.
You are there to find out what the interviewee knows and how she/he works, and to present the educational program and policies of your school and see if it is a good fit. None of that has the slightest thing to do with what anybody is wearing (at least, I sincerely hope not!) Be neat, clean, and appropriate to the general formality level of the school — if other people on the teaching staff wear jeans, you wear jeans, and if other people wear tailored suits, you do too. If there’s no dress consistency, wear something as neutral as possible that fits either formal or casual, simple pants and nice shirt. Your clothing should definitely not be revealing or sexy, although you also don’t want to attract attention by going to the other extreme and covering yourself in much more than the community standard. Go for quiet colours and little or no jewelry. Everyone should be looking at the speaker in the group, not the superficials.