When I visited BCFT prior to making my decision on training provider, the students on the course at that time appeared to be in a mix of anything from casual to smart. Dena told me the head of traning's view is that it is far more important that the students are comfortable and focused on the training than worrying about what to wear (hmmm, arguments for casual and/or uniform there then). This is in contrast to some other providers, who insist on "uniform" of some sort or other, but then other providers I visited who did have dress standards seemed to have students with various interpretations of these standards!!!!! so not exactly uniform after all!
Personally, I would suggest full flying suits (especially for groundschool!!) or gold braid should be avoided, but anything else should be fine.