it differs alot on my campus
round one:
Chi Omega: Chapter jerseys and jeans or shorts (I can't remember it was casual and HOT outside)
Tri Sigma: Badge wear, but nothing too dressy. everyone was mostly in nice day dresses and skirts wearing thier badges.
AST: They were dressed similarly to Sigma. Dressy day clothes and badges
as far as everyone matching goes...
round two (philanthropy):
Chi Omega: in white button up collar shirts (long and short sleeve), badges, and some sort of khaki colored pant or capri (shoes, I don't know)
Tri Sigma: White with purple Sigma letter shirts that they had all made (they were cute) and jeans (we were down on the floor making stuff)
AST: they were all dressy casual (in khaki or black pants I think)
I do know that as a PNM it is always eaiser to remember what sisters are wearing if they are wearing the same thing, but I don't know if remembering that sort of thing sways anyone's mind. i think it does make a good impression to come off as a unified group, but you don't have to do that the first night. I prefered the different dresses my first night because I didn't feel overwhelmed by a sea of uniform colors. We were (the sisters and PNMs dressed similarly, so it made me feel more comfortable. However, every school is different.