Those pieces are much more elaborate than the ones I painted.  I also recognized that at this scale, historical accuracy is just not a priority.  Also for me I wanted them to use the idea, “This color goes to this nation” sort of approach.  My most elaborate ones are for the Japanese.  Back when I was playing Revised, I also wanted two colors of UK troops because of the temperate and tropical environments.  I may have painted Marines for the US in the Pacific if I had stuck with it long enough.
For the Japanese, I used three colors for “bodies”, sand, IJN Green and IJA Green.  I added a lot of meatballs and silver for glass on the fighters.  I also painted the lower hull of all ships with Battleship Grey.
The UK were painted either a regular green or a color called Armor Sand for tropical uniforms.
The decks of US warships were painted “wood” and the superstructures were painted battleship grey.
Russian Pieces were colored a pale brown.  German pieces were colored European Grey.  Chinese pieces were going to be a dark brown.
Now I have a new challange to find colors for French, Italian and Aussie pieces.