I generally prefer the Klingons in the original slate grey as shown in TOS and SFB.
Green is more the livery for the TMP period, but is a different green to the one used on the Klingon ships is a lighter shade.
TOS Fed ships are US Navy ghost grey, though by TMP, this has lightened up to a more whiter colour or grey.
The TOS and TMP Fed ships are pretty uniform due to Star Fleet's modular design policy, to aid supply and logistics. This seems to have gone out of the window by the TNG period.
Starship, like aircraft, millitary and civilian, have always been built around whatever new powerplants that had been developed. That's how aviation has progressed throughout current history.
In Trek star ship designs are built around the latest Warp Nacelles and the size of the Warp Core that powers them (or it, in the case of single nachelles).
In TOS, for the Feds, there is the PB32 through to PB47 series of nachelles, with LN64 for the TMP period, the LN50 nachelles for the TMP to pre-TNG period, but in TNG and after anything seems to go for Fed star ship nacelles.
The thing is the millitary doesn't diversify as it makes logistics, maintainance and re-supply a nightmare. They evaluate the most efficient designs, select what they're happy with and build their logistics systems to serve these designs.
Thankfully, the Klingons have stuck with the S-Graph nachelle design from the D6 shown in ENT through to TNG, but have also introduced newer nachelle designs in parallel.
The Romulans, er, well they're on a technological learning curve quest, as they start out well behind the other races in the Warp Technology race. They're still using Sub Atomic Impulse Power to power their Warp Drive in early TOS episodes and buy in MAM technology from the Klingons, which they then have to disect and learn the science of even through to TMP. By TNG they seem to have it well figured out.
The Gorns.... again a Modular design philosiphy, though their nachelle design allows entended length as extra Warp Coil sections are added as required, which is a good concept. SFB has introduced the "Broad Hull" designs which are standard hulls built with a centre section to "stretch" them width wise, in order to keep up or ahead of the ISC.
The Kzinti have the same extendable nachelle design dating from pre-ENT through to TOS, which means that they're rapidly falling behind in Warp Technology, as a nachelle can only be extended with additional coils so far. The general need for three nachelles on Kzinti warships.
However Mudd's TMP cruiser has dragged Kzinti into the 23rd century as far as Warp technology goes, and hopefully a whole new TMP Kzinti fleet will spring from ths new design.
The Tholians are limited by their shipyards being only to build Police cruiser sized hulls that have to be welded together to build larger ships.
However, they can build Dreadnaught command sections, so perhaps new designs would develop around secondary hulls to power these.
The Lyrans.... again they extend their nachelles as and when required but are are also less Warp technologically backwards than the Kzinti, though this doesn't give any adtvantage over them.
The WYN are unable to develop their own technology and so have to rely on what Warp technology that their neighbours will trade with them.
The ISC.... well developed and advanced. All ships built to a formula rather than a modular design. It has proven to be successful for them.
The Orions are also limited in Warp technology and this limits their star ship designs. Unable to gain new technology from other races, due to the other races not liking them, and that star ships captured in battle are usually so badly damaged that gaining Warp Nachelles and Cores through this route fails. However, they were able to recover the secondary hull of a D6 after a lucky hit destroyed the neck and detached the command section. The non-Klingons promptly mutinied and surendered the secondary hull to the Orions. In the Orion shipyards a Battleraider hull, complete with Warp Drive (for seperation and power), was added and the OK6 came to be.
However, the Orions aren't capable of duplicating the S-Graph engines or Warp Core.
However, concocting interested Orion star ships attached or powered by various various parts liberated from other races.
I can see the point though, that the Feds do seem to be lacking any sensible design polcy with all the TNG models that are appearing. There seem to be a lack of uniformity though a vague formula seems to exist. Nachelles, however, seem to be varied and non-uniform on most.
I would expect Fed TNG runabout design to use the same nachelles as other runabouts in service.
Having uniform colour schemes for the right period for a race.
At least the Kzinti / Mirak have the same uniform rust colour.