Windsor uniform

The term Windsor uniform is the name of a type of dress worn by male members of the Royal Family (and very senior courtiers) at Windsor Castle.
The uniform was introduced by George III in 1779. The full dress, which had a good deal of gold braid about it, did not survive beyond 1936, but the undress form is still worn today: a dark blue jacket with red facings. It is now worn only at Windsor Castle, and since the reign of King Edward VII has generally been worn only as evening dress (though Charles, Prince of Wales has worn a version of it as a riding coat).