There is no particular clothing etiquette for Gypsy Cobs. In England for a show you would be expected to wear white or Creme jodphurs, black long boots (well polished). a white riding shirt with tie or stock, black or navy show jacket and a black riding hat and riding gloves. However, if you are riding a 'Heavy Horse' (large draft above 16hh), you would wear creme or yellow jods, tweed hacking jacket, black long boots and the shirt or stock. I don't know how strict they are in the USA but in England there is a lot of snobbery (which I hate) and you have to be turned out to perfection. Good luck with your show.