What one wears is not a big deal as long as it doesn't stand out for the wrong reasons. Like when someone shows up in a completely wrong sized suit, or wears formal attire instead of a standard suit, or just wears a button down shirt, or wears street shoes with their suit, or how about showing up to the applicant tour and lunch wearing a polo and jeans while the other applicants wore suits (they weren't interviewing that day, but interviewed in Spokane and were checking out the Seattle campus). All those have happened in the three years I have been here. But if you just do the standard, a charcoal or blue plain suit and basic patterned tie, you'll be fine. You want to be remembered for your interview, not your outfit.