1. The color of the uniforms most likely came from Roddenberry(mind you, this is only speculation on my part) as they for the most part were similar to what he had put together for the original pilots of TOS, "The Cage" and "Where No Man Has Gone Before". In those episodes, there were muted versions of gold and blue, along with a vague beige color that would eventually become red. In TMP it's back to muted blue and gold, with some presumably enlisted crewmen getting the chance to don pure-white.
2. The variety of outfits was probably due to a vastly superior budget compared to Television(Phase II footage I've seen is much more traditional to what TOS had to offer). It also better reflects the variety of attire available to officers and servicepeople in virtually all Armed Services at that time and now. You can go traditional long-sleeved, you can go casual short-sleeved, you can even deign between a two-piece(traditional) or one-piece(a one-sie type jumpsuit) style of uniform.
3. The changes from TWOK and beyond did not come from Rodenberry, but rather the director and creative staff put together for that movie, with a far greater emphasis on Nautical-Military style. I've read Nicholas Meyer's book, The View From the Bridge, and he had a rather notable distate for the "Dr. Denton-esque pajamas" used in TMP, not to mention the overly clean and almost-recreational look of all the ship interiors. Of extra note; the TMP uniforms, most of them, got a red dye job and were used for crewmember jumpsuits throughout Movies 2 through 6.
4. Back to TMP, there was an annoying factor that the shoes were basically sewn into the uniforms themselves, presumably another Roddenberry creation(dude HATED to see zippers and the like in plain view of the cameras). This was wisely ditched by TWOK for obvious reasons.
5. I was surprised to find the rank stripes from TOS were in fact preserved and used in TMP. I had initially believed said rank was located on the tiny shoulder straps(which, yes, they are, and they're most helpful when someone is wearing short sleeves), but I wasn't watching the cuffs at the time.
6. The extra budget also allows for greater elaboration of designs that simply were either unavailable in TOS or may have been cobbled together poorly. Engineering's Environmental Suits and the Space Suits, both in the aborted 'Memory Wall' scene and in the final product, are sterling examples of this. Even the jumpsuits look more like actual jumpsuits instead of the paper-gi extras had to throw on when uniforms weren't available. The Security Armor miiight have saved a few dozen lives on TOS. The Field Jackets as a concept came from The Cage, but were never used beyond it. They functioned about the same. As did the wrist communicators, which I don't think survived beyond TWOK...?
7. Can't forget the Admiral's Uniform either(yes, it's an actual uniform for Admirals; Kirk's rank braids are one thick Commodore Braid plus one more braid... while after he's taken command of the Enterprise, he goes back to the traditional two-full one-part rank of Captain). I imagine in a ensemble that was unfortunately dulled, that two-color look easily stood out as the best of the lot. In fact, it looked so good that one could imagine it standing alongside the actual color schemes of TOS had they been utilized instead.
8. One final notation, about the chest emblem. You may have noticed the circle behind the chevron, and how, for different characters, said circle is different colors. This is a more detailed separation of various fields and services, doing away with the three-field broad display of uniform colors of TOS, and the four separate symbols that were on the chevrons during that time.
