I never hated the green shirt, but I was definitely under the impression that it was the only one in wardrobe. That there weren't multiples, in the back, somewhere.
I would think there was at least one spare copy of the costume, so a show could finish filming after a coffee spill. Also, there were three different versions of it, in the first two seasons, as its look evolved.
What I don't like about Kirk's green wrap-around tunic is that it shows too much skin with its plunging neckline. You never see that in professional or military men in real life, when they're dressed for work. "The Trouble with Tribbles" is one where I
really notice the skin exposure, and it doesn't work for me (but I like that episode).
The first green wrap-around was created to highlight two different Kirks in "The Enemy Within" (E5). Then apparently they put the wrap-around tunic into "Charlie X" (E8) for variety, and that was a fiasco because they didn't plan for it properly. Kirk gets on the elevator wearing one shirt and arrives on the bridge wearing the other.
The wrap-around would not return until "Court Martial" (E15), for all of Kirk's scenes in Stone's office. This causes Kirk's shirt to switch back and forth during the episode, but there's room in the plot for him to be plausibly changing clothes so as to be dressed up for the commodore.
Maybe in E15 they felt that literally having gold braid on Kirk's shoulders would give him more authority, more presence, in the meetings with his superior. I wonder if Shatner himself suggested it. He would no doubt have remembered all that gold on the uniform from "The Enemy Within," and he was famously astute at visual drama.
Appearances of green wrap-around:
Version 1:
E05 The Enemy Within
E08 Charlie X
E15 Court Marital
Version 2:
E35 The Doomsday Machine
Version 3:
E36 Wolf in the Fold
E38 The Apple
E39 Mirror, Mirror
E41 I, Mudd
E42 The Trouble with Tribbles
E43 Bread and Circuses
E44 Journey to Babel
E48 The Immunity Syndrome