A black show coat, white or beige breeches, tall boots, black gloves, hair in a hair net or a show bun thinggy, black helmet, stock tie or collar with a pin.
Any colored breeches, your choice - anything goes. Top, can be long sleeved, can be a t-shirt, polo, whatever you choose. Safety vest. Gloves. Helmet, tall boots. Hair in a hair net, or in a bun or a pony tail or braid, whatever - anything goes.
Black show jacket, or dark colored. Forrest Green, Navy Blue - but it has to be dark. White breeches or beige. Tall boots. Show blouse with a collar and pin, black gloves, black helmet.
Pretty much what everyone else said, but if its a schooling show, which i'm assuming it is, especially if its in the summer, a jacket isn't THAT necessary. I never wear a jacket to a schooling show and most people don't sometimes you will see people with jackets at a schooling shows though. Ha. For summer schooling shows I just wear tan breeches, tall boots, gloves, and a white polo tucked in with a belt for all 3 phases. Or I might change into a colored polo for XC. If it's recognized definitely go with what the others said. Just saying this because if you don't have a show coat and everything and this is your first event, unless you KNOW your going to keep eventing as long as its a schooling show you don't really need to go out and buy all that stuff yet.