I remember the ZTAs at my school wore white dresses with turquoise sashes. It was very pretty.
You could also do light green dresses. That would be summery.
Does UCLA still allow you do all matching? It won't be hard to find a uniform summer green. You can take some liberty with your colors-- it doesn't have to be specifically "AEPhi Green." Maybe a sleeveless tea length dress in celadon or seafoam, or lime? You can decorate with lemons and limes as centerpieces, if you have any tables. It will look summery and elegant and suitable for daytime, a little retro and very memorable.
Hope this helps! Regardless of what color you choose, it will be hot. You may want to consider cutting your outdoor ceremony plans a little short and taking things inside where it is cooler.