Page "Eventing" Paragraph 154

For the intermediate and advanced levels, dressage attire is similar to that of Grand Prix Dressage.

The rider must wear a dark coat ( usually black or navy blue ), with a shirt, stock tie, and pin.

If the rider is riding at FEI level, only then can they wear a shadbelly tailcoat and a top hat.

Riding breeches are usually white, although any light colour is permitted.