Found the post below and had some thoughts that warranted a new thread. It would seem that the deflector dish in TMP has at least three modes: not-illuminated when in drydock, orange when main drive systems not engaged, blue when at impulse/warp. The directors cut tried to fix some shots to fit this system, but made others not consistent. Supposedly Probert had said that it gets bluer and maybe even eventually whiter as power goes up. So then, why after TMP, and the parts of TWOK that re-use that footage, do the Enterprise and Enterprise-A never show onscreen with a deflector color other than blue? What do people think? Both in-universe and real-world answers from anyone with info would be welcome.
In-universe? Since it also is part of the long range sensor system it could be blue all the time just doing scans. I don't consider it the only navigational deflector the ship has for flight so the color doesn't have to tie to it's flight mode.
Not a bad idea. But what I'm trying to ask is, why is it able change color at first but then for 4 movies it is always blue? (other than the distinct possibility that they were just saving time on setting up the shots that way)
For a behind-the-scenes reason, a lot of the special features for the TMP miniature were never used after the first film. Open shuttlebay, all the hatches at the bottom of the saucer, the color of the dome above the impulse engine (only seen glowing red when the impulse engines are turned on in that movie, and off when under thrusters or warp, but glowing white all the time in the later movies, though typically depicted as blue in fan-art and other secondary sources). Pretty much the only things that stuck were the warp engines, the torpedo tubes, and the standard windows and flashers. Even the spotlight setups were much less complicated, and sometimes a little weird (the middle movies lighting up the pennants on engineering with tight stencils illuminating only the pennants, rather than making it look like there was a spotlight coming from the saucer or nacelles). Either the lighting system for the deflector (and impulse dome) was damaged while the model was dismantled then unpacked for TWOK, or it was just regarded as too much time and trouble to deal with (I have no idea, for instance, if there were separate blue and orange bulbs and you had to open up the model to switch back and forth).
I thinkg David cgc is right on the behind-the-scenes answer. Another in-universe possibility is that the dish color varied because the Enterprise's dish was an early new style of dish. Later models of that dish were standard blue. That way we can explain why TWOK also could change colors (re-used footage) in that it was the same model dish.