Although both our daughters dressed differently from others, both of them got offers from CU. That reinforced me that formal dresses are not necessary so long as you dress properly.
I remember that when my daughter was asked by Cambridge to attend an interview at Cambridge (UK), it mentioned that formal dressing is not necessary. He/She should wear comfortably for otherwise it would affect her performance in the interview.
I think it is also applicable to the applicants in Hong Kong. They do not bother to wear formal dressing but dress comfortably and properly.