I know customs vary from place to place but when I graduated from Glasgow University kilted I wore a jacket. Strictly speaking I should have worn my tweed argyle as it was a morning ceremony, but I went along with the custom that graduands who are kilted wear a dark PC and vest with bow-tie to graduate. UK academic gowns are generally open at the front, also receiving the hood of your degree and being 'capped' by the University vice-chancellor is when your status changes from graduand to graduate.