"Why Gold, Tan,- or whatever colors those shirts were supposed to be - Tenne, Khaki?";
and,
"Why the appearing-disappearing-re-appearing Green?"
Much over-emphasis and use of color was happening in mid-sixties television, and in an attempt to capitalize on the new "IN COLOR" advance in technology. So, if you were creating a new show called Star Trek, and you were going to design it to capitalize on the color technology waiting on the doorstep of America, it seems to me, that the most obvious answer would be to go with the Primary Colors - being: Red, Yellow, and Blue - in order to maximize on what color television cameras and color television sets "see" well.
Okay, so I'll hazard an unfounded guess that Yellow looked too bright, unflattering, unheroic; or perhaps simply didn't shoot well or reproduce well under studio lighting conditions - who knows - not me;
however,
Gold become a powerful and dignified substitution - imho - for big-bird Yellow. So to me, everything makes good sense so far; if using the Primary's [with the chosen Yellow substitute] as your guide in decision-making;
but then,
We get this Green Captain's shirt - early-version - which may have been chosen to distinguish the captain from the rest of the crew; and, make the Star-of-the-Show stand out to the audience; with which, if that was the reasoning, makes sense to me;
but then,
the Green is replaced by the Gold/Tenne; and then, the Green Captain's Shirt shows back up - other-version - disappears, shows back up, and, disappears again - round and round.
Now, there has to be an in-story behind all of this; being, one I would like to know.
If you put square brackets and an s -- [ s ] without the space -- it will go striked out. I suspect you typed color(s) but with square brackets
I've removed it in the above quote to make it easier to read.