Didn’t Picard usually overrule Riker and beam down, anyway? “Captain’s prerogative, Number One. Make it so.”
Gold is actually green. The Federation has many alien members that probably don’t see colors like we do, especially given different planetary studio lighting and cameras. So, who knows what Star Fleet style consultants have to deal with.
Even the M5 unit didn’t like Kirk’s landing party choices. But, it’s his chance to get away from the ship with his buddies, so give him a break.
The OP is just wrong. Uniforms change all the time, even in stable bureaucracies. Even language changes. Heraldry changes as well, due to political shifts at various scales.
Extrapolating from your relatively conservative 20th Century national army to a 24th Century space navy for a growing federation of planets is a little unimaginative. Picard’s Starfleet is experimental enough to make its flagship a flying city with crew’s families aboard. It includes planets and even species that weren’t in the Federation in Kirk’s era. There may be political reasons for the change you don’t even know.
Starfleet, for whatever bureaucratic reason, changes its uniforms a lot. The color-coding from TOS era reappearing in TNG era a bit scrambled is really not that odd.
One could, I suppose, claim that as new species joined the Federation their color traditions might need to be dealt with, ‘WTF? That’s a hookers hue on my homeworld.’
Starfleet might be a military, but it isn’t the US military. The US military was bombed into nonexistence during WWIII and the Post-Nuclear Horrors. It collapsed into factionalism at best and, more likely, outright banditry and warlordism. And this isn’t even fanwank: It’s canon from multiple series and a couple movies, at least.
So the entity that launched the various iterations of the USS Enterprise wasn’t the USA any more than France or Germany is Rome.
Maybe in the future, human’s aren’t so concerned about silly traditions/conventions.
What makes you think they’d use the colors of the US military?
The Federation is, after all, a single Earth government. Why choose the US? Why not India? Or France? Or, as would be likely under the circumstance, a color scheme that wasn’t identified with any particular government.
Considering that replicator technology basically turned the entire Federation into a Post-Scarcity Economy, I’m surprised that any traditions survived.
I never said they’s use the heraldic colors of the US military. I said they’d remain consistent to the Federation’s colors. They start talking about swapping Gold and Red and EVERY senior captain and admiral in Command and Engineering is going to gripe. And every retired Captain and Admiral too. And the retired ones are going to complain to elected Federation officials. And to Federation veteran’s groups. And to the press. And retired Admirals end up on Boards of Directors. And as Deans or Presidents or Chancellors of higher educational institutions.
The Army Blue uniform should have stayed a full/ceremonial dress uniform like Marine Blues, or at the very least they should have come up with a buff shirt (the historic contrasting color) for everyday wear and a way to visibly switch the coat from office-dress to ceremonial wear.
Although to be fair, historically ceremonial dress was just the “business” dress, but blinged up (this is so for the Navy, CG and AF).
And just today I rode the DC Metro into Capitol Hill sharing the car with what must have been half of some USAF command’s staff and they were all wearing good old AF blue.
And they changed the uniform emblem from one for every ship to the Enterprise emblem being used to represent every ship and Starfleet.
I know I’m reviving a dead thread, but having just watched season one of Star Trek: Discovery I have thoughts about Star Trek uniforms.
See, for this and other kinds of gripes about Starfleet based on the experiences of real, contemporary (especially U.S.) military service, I think it completely misses one of the major points of Star Trek.
Starfleet is not part of the legacy of U.S. or other current military traditions. It has some of the trappings of them, but it’s part of a very different culture that has grown out of a unified and peaceful Earth and subsequent peaceful integration with alien races.
So when it comes to Star Trek, I don’t think it’s valid to say things like “every senior captain and admiral is going to gripe” based on personal experience about what people in real, contemporary military organizations gripe about. They’re a different society and a different civilization, with a different experience than we have. Maybe they just never learned to care about things like heraldic traditions?
This is a basic fact of Star Trek, that their uniform details change frequently and drastically. It’s just something you have to expect.
Look at the way rank insignia changes wildly.
TOS and TMP: sleeve cuff stripes, like traditional navies
WOK and subsequent movies: Weird little icons on the shoulder straps that aren’t recognizable as contemporary rank symbols
TNG and subsequent: Pips that keep moving around to different places
In Star Trek, we’re watching a culture that is accustomed to drastic changes in style for these things. That’s part of the ethos.
Maybe they shouldn’t be called “uniforms”, because they aren’t… you know… uniform. 
The reason for the change I think matches the real world. There was a point in between the two eras where everyone just wore red. So I think the colors got mixed around.
Plus, I bet the redshirt stereotype even permeated Starfleet. Maybe that’s why uniforms all became red. And then, when they went back, security refused to be red again. I mean, red is proven (for Humans at least) to be the most noticeable color–maybe they didn’t want to be a walking target anymore.
And it seems to have worked: there was never a replacement of redshirt with goldshirt as the ones most likely to die.
Can you imagine the nightmare of getting intergalactic agreement on something as ultimately inconsequential as uniforms?
Maybe there was a memo sent around after a particularly exasperating round of fabric negotiations:
Starfleet Command Memorandum 675487980878065
Re: Starfleet Uniform Intergalactic Re-Standardization, Stage CXCLXVIII
You know what? Fuck it. Just… fuck it. I’m done with this. Wear something, OK? I trust you.
BTW: Those are not Roman numerals, that’s the abbreviation for the committee chairbeing’s favourite uniform colour. It’s pronounced the same as “Valve”, except miss out the L and the A.
Star Trek’s made up. I think they made up good colours, even if they don’t fit with what current-day earth military might have done. (that mustard yellow would look horrible on Patrick Stewart, you can’t have your main actor looking like he’s just stepped out of a crypt.)
I’m still waiting for the crew of the Enterprise to be put on trial by the Stephen Jay Gouldians for continually misusing the word “evolved.”
The courts are clogged with every SF movie and TV series ever.