Speaking of the skittle thing, two years ago for Formal Recruitment we had our "Teddy Bear Picnic". We had t-shirts made with teddy bear material for our letters. The t-shirts were different colors (blue, yellow, red, and maybe one other color). What was funny is that I think they might have actually signified our "bumping" groups, but I'm not sure. Anyway, it was really cute and showed a little uniqueness (about as unique as you can get during Formal Recruitment).
If you guys do a fun theme, my favorite every year has been "Island PHI-ver". We got cute shirts that said "Island Phi-ver" on them and wore beachwear, like sarongs, board shorts, flip-flops. I always like seeing what my sisters show up in and I think it's our most fun party. We decorated with beach towels and stuff like that. It's super cute!