Formal Hunt Attire is worn during Foxhunting Season- During the winter months generally. There are very specific rules that would take a month to get into- so here are just some general things to keep in mind:
A black or Navy heavy or light wool hunt coat. A white shirt with white stocktie and a plain stocktie pin. The stocktie should be tied accordingly so that in an emergency it can be quickly taken off and used as a flag, bandage, etc… **Again- foxhunting apparel is beautiful but it designed for practicality. You may wear a canary or tattersall vest for extra warmth, buff colored breeches, and black tall boots- with no flaps is preferred. Black or brown gloves and a black helmet.
For more specifics- please read what the Master of Foxhounds Association has to say. You can also check with the hunt you are going out with and for any other specific advise, ask around within the hunt for someone who knows all the specifics on Appointments- there are always a couple helpful hunt members.