The USMC fatigue tops are too varied. When Carter is auditioning the men only Gomer's and Martoni's left pockets have the Marine Corps emblem. Martoni's is faded and Gomer's pocket flaps aren't buttoned as they should be. Also Higgin's pocket flaps are cut straight across not in a "V" shape as the other's are. Then later when they're practicing on stage there are a couple more men with emblems but Gomer's has faded.
When the men perform onstage in their brown dress uniforms one of the men's shirts is colored a bit gray and doesn't match the rest.
The choir tries to hide its rehearsals from Sgt. Carter, who ultimately hears them rehearsing in the bed of a covered truck.
However, the men would have been sitting in total darkness and would not have been able to read their sheet music.