It really depends on what you plan on doing for the evening. Are you just planning on hanging out on the beach or are you paying to go to one of the nicer hotel parties? If you are just going to the beach then casual shorts are acceptable. If I were headed to a hotel party I would think white pants with sandals are acceptable. Most everyone heads to the beach at midnight and it is HOT and stuffy so go for light weight fabrics. Women have it much easier, breezy white sundresses with a statement piece of jewelry.