Le sigh! A reply!
To paraphrase, though nothing concrete:
Federation and Klingon ships likely got their color from custom mixed auto paints. My read is- custom mixes bought in a good quantity, then stored for the inevitable call.
Others were very likely off the shelf. Model Master or 'railroad color' which I always read to mean Floquil. Floquil was still available in the early 2000s in its original formula, though the color consistency was, unbelievably, even worse then than it was in the 20-30 years prior. Still, up to the end of the original mix's run, it could not be beat for its flex, and damn near working with impunity with it. Best model paint ever. Too bad it'd kill you.
So not much in terms of specifics, but I'll take a confirmation of the usual suspects and another vote to, in essence, get on with it and build colors that match and alter correctly in the varying lighting scenarios, to the best of one's ability.
Onward. ;-)