Officers in the 18th Century were often attended by servants, and their dress is a fascinating study. All images are contemporary 18th Century paintings with information where applicable. Clicking on an image will enlarge it.
1752 "William Kerr, 4th Marquis of Lothian" by David Morier.
This Marquis of Lothian held commissions as Colonel of the 24th Regiment of Foot and as Colonel of the 11th Dragoons. He is wearing the uniform of the 24th Foot. What is of interest to this discussion is the young man just to the left of the horse. He wears a short white coat with white breeches and stockings. Underneath the coat is a blue waistcoat (presumably) and very unusual yellow garment. The yellow garment could be a waistcoat but it has fringe at the ends, along with gold embroidery. It is also possible that it is a type of apron instead. His cap is of a type similar to that worn by dragoon musicians. It bears a sun in splendor under a crown, and has white scrollwork on either side and is trimmed with yellow feathers and a black plume. The young fellow carries a stick with a silver head and not an instrument--an odd omission if he is intended to depict a member of the regimental band.
1780 "George Washington" by John Trumbull.
In this painting, George's horse is held by a servant, who is possibly William "Billy" Lee. He wears a red turban with a red plume. His jacket is dark blue with red cuffs and his waistcoat is red. Unfortunately, the large horse obscures the rest of the detail. It is fairly likely, however, that his breeches and stockings are dark as well.
1781: "Marquis de Lafayette" by Jean-Baptiste LePaon.
1782: "The Earl of Aldborough reviewing volunteers" by Francis Wheatley. At least one servant is pictured, sitting behind the center carriage. He wears a white turban, blue jacket with white collar, adorned with an silver epaulette and silver-laced buttonholes, buff breeches, white stockings and brown shoes. The epaulette, setting, and general similarity to other officers' servants' uniforms suggests that he also performs this duty.