Over the years I've collected more than 100 colours in my Paint Shop Pro palette, 90 or so of which represent WW2 GV and aircraft colours. The original sources for these came mainly from skinning, modelling and colour matching websites as well as paint swatches found on the web. The various lighting quirks of AH3 have caused me to modify many of my swatches recently, adjusting the darkest and lightest ones closer to mid shades. I'm happy to share any of my colour choices with any other skinner but in the end they are just my opinion of what looks right.
I think any stickied post should be for all WW2 colours, not just US ones. If anything the US colours with their FS and ANA numbers are the best documented, its Japanese and Russian colours where things get really murky. I'd be happy to contribute to that thread but only on the basis of it being an aid for skinners, not as a mandatory requirement for future skins.
It's too complex a subject for a mandatory list:- The colour of WW2 paints could vary considerably over the life of an aircraft due to ageing. Different paint manufacturers were sometimes used by the various factories making an aircraft, for instance Zeroes made in Nakajima's factories were painted in different shades of green and grey to Mitsubishi's. The specification of US Olive Drab was changed mid war but not all factories used the new shade. Researching this sort of stuff is part of the fun for me.