Even though i'm not a florida gal, i wanted to add my suggestions...i totally agree with aephi alum, it's always good to stand out color-wise because sisters will be able to recall you immediately as someone who stood out visually....and i would err on the side of dressy-ness; the potential new member recruitment wardrobe for my school sounds similar to yours but we usually see girls in skirts and nice shirts on the 'casual' days rather than shorts and t-shirts. RCs always tell the girls that you always want to look your best, so i don't really see the problem with going for a nicer look unless it's a ball gown or something
good luck!