 The frock coat, often attributed to the result of the fashion influence of the Regency dandy George Bryan 'Beau' Brummell, was almost universally black, and was worn with waistcoat and trousers, which could be of any colour.Black coat, waistcoat, and trousers - "frock suits" - were worn only for funerals (as a 'mourning suit') and the most formal of occasions.The trousers that went with it - what would be known as formal trousers - could either be checked or striped, or have no pattern at all.