Iv'e been putting red (civ coloured) stars on my russian tanks and when I redo my german units (stuka and king tiger) for my mod, I'm going to give them civ coloured ares (with grey as thier colour, germany can have grey coloured camo. If other civs, use german designed units; Roumanian cavalry, Finnish panzers etc.. they can have other coloured patches; dark red, white etc..)
In the txt explaining the improvemnts to the latest patch it said that all the civ colours would be better suported (it used to be that using any colour other than the first 16 or so would cause the game to crash) I have not tried this myself yet, but the later colours 20+ have good potential as camoflage colours.
It would be necicary to actualy find out what colour each nation used for its uniform camo colour circa WWI/WWII
Of course this would only work if you were producing the units specificly for a mod (the reason why I have delayed the release of my light and heavy civ coloured tanks) otherwise you get pink french tanks and bright green greek tanks.