Wear the same clothes that you would wear for residency interview / job interview. It is not time to "stick out." In fact, I believe more conservative color schemes are important - even more than a residency interview (no bright yellow or white suites). While your answers are critical in the exam, there is no doubt your attitude and personalities also play a role in this test. After all, they are looking to pass people who know there stuff and care about helping people (people who will represent the profession well).
In other words, this would not be the best attire in my opinion:
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