Found it. Here's the part of the text for the plate dealing with the uniforms:
"Custer's 'Wolverines' largely wore the Union Army's regulation cavalry uniform . . . . But as in other volunteer organizations, officers tolerated a certain amount of individual expression in their men's dress. Quartermaster Sergeant Sam Brownson of the 5th Michigan cavalry sported a plain jacket with no trace of yellow braid. After Trumpter John W. Cunningham enlisted . . . he received a rather unique musician's jacket. The collar was cut shorter than usual, while the cuffs bore no yellow lace and each was closed by four brass buttons--rather than the normal two. Cunningham also had yellow stripes half an inch wide along the outer seams of his trousers. The Michigan Brigade's most conspicuous article of dress was the red necktie which all ranks adopted out of admiration for the flamboyant Custer [who wore one]. Philip Laboe, the brigade's forage master, proudly posed for a photograph in a zouave-style jacket and a Custer tie."
A footnote states that "this plate is based mainly on photographs in private and public collections and the eyewitness sketches of two Civil War combat artists, Alfred R. Waud and Edwin Forbes."
The text was by Dr. Gregory J. W. Urwin, who authored a book about Custer's Civil War career, and the artwork was by Clyde A. Risley of Imrie/Risley Miniatures fame.