This is from DD's university:
We advise candidates to wear a light coloured shirt or blouse with dark trousers or a skirt. A buttoned shirt or blouse is recommended as there is a loop on the academic hood which can be affixed over a button. Alternatively you may wish to bring a safety pin to help hold the hood in place. Traditional and national dress is encouraged.
However, all the girls wore dresses, quite a few being quite the opposite of conservative. One girl nearly fell out of her dress as it was so low cut.
I admit that I had to google sub fusc because I didn't know what it meant 
It comes from the Latin meaning dark brown.
I have just lifted this from the university of Oxford's website:
Full academic dress should be worn at all formal University ceremonies including matriculation and degree ceremonies. Sub fusc (from the Latin sub fuscus meaning dark brown) should be worn beneath your academic gown and is also required when sitting examinations.
You are required to wear your preference from the following as sub fusc:
- one of:
dark suit with dark socks, or
dark skirt with black tights or stockings, or
dark trousers with dark socks or dark hosiery
Socks, tights and stockings must be worn and must cover the ankle entirely. There should be no gap between the bottom of the trouser leg or skirt and the top of the socks or stockings.
- dark jacket, if required - worn underneath the gown
- black shoes
- plain white collared shirt or blouse with sleeves
- white bow tie, black bow tie, black full-length tie, or black ribbon.
PLUS:
the appropriate academic gown (see below; Academic Gowns for Students)
mortar board or soft cap
Can you imagine wearing all that lot during summer exams?