I like the TMP uniforms. The blandness of the colors is something of a myth, arising from the fact that all the home-video versions available for two decades were based on film-to-video transfers that washed out the colors severely. The Director's Edition is digitally remastered and thus represents the more vivid colors of the original film. (Important to remember that, contrary to the recent abuses of the word, a "remaster" is a new print taken from the original master print, and is therefore as authentic to the original as possible.) The colors are hardly garish, true, but they're not as bland as people think. For instance, the uniforms that look gray in the washed-out video transfers are actually more of a slate blue, and the medium brown-appearing ones are more of a mustard hue.
And I agree with the comments above; why
would military duty fatigues be brightly colored? Look at the colors of real-life military fatigues: khaki, tan, gray, black.
As for the TWOK uniforms, I think they're ridiculous. I could buy them as formal dress uniforms for special occasions, assuming Starfleet was on a historical kick and considered it fashionable to dress up like something out of the Horatio Hornblower era. But it makes no sense for the crew to wear something that ornate and complicated and anachronistic as everyday duty wear. Now, if you ditched the jackets and just went with the undershirt with insignia and rank pins attached, that could work; in fact, it would be very similar to the pilot uniforms. But wearing the whole elaborate getup as a matter of routine just doesn't make sense.
Do you really believe it was that and not simply more of Roddenberry's teenage male approach to sex through which he tried to shoehorn as much cheap romance novel crap into Trek as he could? I suspect the latter. And running around naked would demonstrate a more mature society? Clothing has a wide range of utilitarian functions beyond simple modesty and I doubt it's going away no matter how "mature" our society becomes about sex. No, I think Roddenberry just wanted to be able somehow work naked women into Trek.
Whatever Roddenberry's proclivities, he was hardly the only futurist of his era to propose that current nudity taboos would vanish in the future. It was a fairly common prediction in science fiction of the '50s, '60s, and '70s, and possibly later. In Larry Niven's Known Space, for instance, nudism was a legally recognized practice that anyone could engage in with the proper license. It was a natural enough extrapolation from the Sexual Revolution, and from the steady erosion of nudity taboos over the past century or so. In Edwardian times, legs were considered so obscene that you couldn't even show the legs of a
table. Today, we're much more liberal. Just an hour or so ago, I went out for a walk on this lovely day we're having and saw two women casually sunbathing in bikinis that would've been grounds for arrest just half a century ago.
For that matter, America's nudity taboos are hardly global. There are plenty of places in the world where toplessness is perfectly acceptable on beaches or elsewhere. In African culture, there's never been a stigma about showing the breasts (although the legs are often considered taboo). Taboos can change wildly across cultures as well as eras, so there's no reason why it's implausible that a society in the future might be more tolerant about nudity than the present-day United States.
And just because some people choose to go nude in some contexts, say on a warm day, that doesn't mean that clothing ceases to have practical use. It just means that people aren't afraid or ashamed of what nature gave them. And yes, I do consider that more mature than reacting to the human body as though it were something disgusting or terrifying.
Ahhhh!
The reason ST:TMP's Starfleet uniforms came in a variety of styles and colors was simply to let crewmembers express a touch of individuality as a psychological welfare mechanism during multi-year interstellar exploration missions. Similar thinking was, coincidentally, also 
