"Court Martial" is the episode where Kirk wears his green wraparound every time he's in Commodore Stone's office, but changes into his yellow fatigues every time he leaves.
In universe, I say the first season wraparound, with gold braid at the collar, was a middle step between his yellow "Class C" uniform, and the satin full dress uniform. It was a step up in uniform class, like today's officers putting on a necktie to go from the Class C to Class B uniform (Class A adds the suit coat). Thus Kirk was dressing up for the Commodore's office.
Others have said Kirk flipping between uniforms was a film editing issue in "Court Martial." But to me it doesn't play like a mistake.
In universe, I say the first season wraparound, with gold braid at the collar, was a middle step between his yellow "Class C" uniform, and the satin full dress uniform. It was a step up in uniform class, like today's officers putting on a necktie to go from the Class C to Class B uniform (Class A adds the suit coat). Thus Kirk was dressing up for the Commodore's office.
Others have said Kirk flipping between uniforms was a film editing issue in "Court Martial." But to me it doesn't play like a mistake.