It would be interesting to know whether the original plan was to have a large number of different color-panels for distinguishing the "different decks" represented by the corridor set; just the one panel and then set lighting to create the differences, in true 1960s television style; or whether the color coding thing is complete bunk and the intent always was to just go for padded vs. bare... (In-universe, I'd assume Starfleet would have wanted the latter.)
The TMP corridors were done for the film, not p2, so distinguishing between the decks was done when the director wanted it. TMOSTTMP and/or Sackett's STARLOG column mentioned that set decorator Linda DeScenna brought in colored fabric to differentiate the corridor for the Decker/Ilia scene, so it sounds like that was a fairly late call, probably well into shooting.
Doesn't really fit into any 'grand plan' type thinking at all, and kind of flies in the face of the production designer's stated approach to differentiate things or futurize them through lighting. So, in addition to providing some much needed visual snap, the fabric also warms up the scene between the pair, which is probably a big part of the choice, since it is on paper a pretty conventional personal/emotional exchange.
I do wonder about how & why they dulled down the roddenberium metal walls after TMP. Only thought is that like the pearlescent exterior of the miniature, it was just too difficult for ordinary gaffers and cinematographers to light for. As much as I dislike most of the art direction calls for TMP, those metal-like walls are pretty damn impressive.