Horse shows require very prompt and perfect outfits; nothing can be out of place. When in the equitation and the judge is looking at you, they want to see perfection in what you are wearing. Wearing incorrect attire can force you to be disqualified from the show ring.
When riding in a equitation ring you have to check certain boxes when it comes to your attire. You must wear a jacket (navy blue or black), a white collared button up must be worn under, breeches (tan, rust, or even white), a belt, gloves (black or dark colored), and tall boots that fall just bellow your knee. On your head you must have your hair up in a hair net and a correctly fitting helmet placed on top.

If a helmet doesn’t fit safely then you may be disqualified. This is for your own safety because a fall with out a helmet (or a helmet that fits incorrectly) can result in major injury.
Helmets that can be worn in the equitation ring have to follow certain standards, especially if obstacles are involved. A helmet must meet or exceed the safety standards of the American Society for Testing and Materials (ASTM) and be certified by the Safety Equipment Institute (SEI). This standard, known as ASTM/SEI, is a non-negotiable safety requirement for all riders in hunter, jumper, and equitation classes under the rules of the U.S. Equestrian Federation (USEF).
For an equitation ring, jackets must be a subtle, conservative color with a classic, tailored fit. Distracting or ill-fitting attire can negatively affect a rider’s score, as the purpose of equitation classes is to showcase the rider’s skill and position.

Breeches for the equitation ring must be snug, free of wrinkles, and in a traditional color like white, tan, or rust, though some bright colors are acceptable in certain disciplines. For hunters, tan is the standard through and through.
Collared shirts are to be worn under your jacket and must have a collar that snaps in the front to wrap around the neck. They must be white and preferably long sleeve but can also be short sleeve shirts.
As for the boots, they are to be worn in the equitation ring. Tall boots must be polished black leather, fit snugly, and have a distinguishable heel. While both field boots (with laces) and dress boots (without laces) are acceptable, the focus is on a traditional, conservative appearance that creates a long, elegant leg line.
As for gloves and belts, the simpler the better. Gloves should fit well, have some grip, and look good. Belts are something you can have a little fun with. The standard for belts in the show ring can be a little more open. Anything really goes, but sometimes it’s better to just go for a safe plain option.