The standard is white shirts and khaki pants. However, some families like more color with their choices. Pastel colors look nice at the beach but you want to stay away from neon bright colors. If someone wears a really bright day glow looking shirt or pants they overwhelm the photo.
Ball caps, and sunglasses: If you are out in the sun please take your ball cap off occasionally during your stay so the top of your head will get some sun, especially if you are follicly challenged as I am. Same with sunglasses unless you like the raccoon look.