What's that based on?All of The Motion Picture sets were repainted for Star Trek 4, but it's very distinct. There was evidently red carpeting as part of the addition. The corridors, engineering, and the bridge received upgrades at least- all of them based on The Motion Picture sets and equipment.
The ST4 script only called for the bridge, so why would they go to the trouble and $$$ to rework sets they weren't going to use? In fact, in Roddenberry's intro to "The Cage" you can see that McCoy's office is still redressed to be the Bird of Prey room where McCoy speaks to Spock in ST3.