A bunch of us went to C2E2 this past weekend and instead of a rave they held a prom (though for all intents and purposes it was just a rave with more seating). Our group theme for dressing up was to pair our helmets with suits/dresses/etc. If you look through the 405th Midwest socials you'll probably see some of the group photos.
In general, you would probably want to pair the primary color of your suit with the helmet. My helmet is blue, with a black stripe/secondary color, red highlights, and a gold visor. I wore a blue corset vest with a blue shirt, and a black bowtie with a gold detail. Several people went with a gold tie to pair with their gold visors. If I was doing a full suit with a jacket, shirt, and tie, I would probably pair the jacket with the primary color, the shirt with the secondary, and the tie with any detail/highlight color. Then any accessories (watch, pocket square, etc) would also be matched to the tie/detail color of the helmet.
