That is something I would like to know about also. I can tell you that in October 2002 Finesacle Modeler there is a World War II Model Paint Guide which is of some help. Organized by major warring powers, it lists colors, such as under United Kingdom, Medium Sea Grey, and then gives the reference number for brands of paint, if they have something like that. Listed are Gunze, Humbrol, Polly Scale, Tamiya, Testor, Testor Acryl, and Xtracolor Enamel.
I say some help because for example, I am working on a Soviet fighter called the Lagg-3 (66 series). The instructions refer to Humbrol paint colors, and for the underside list a blue shade. On the chart there is a Soviet Union section, a listing for "Underside blue", but a dash for a Humbrol color ( and other brands also ), to say, I guess, there is no Humbrol color for "Underside blue". So I am not sure who is right, the kit instructions or the chart. I partly think the kit insturction is wrong because it also suggests two shades of grey for the top camo colors, but the Squadron Signal book says this plane had a couple other colors for the topside colors, olive-green and something. Or maybe in reality both schemes were used.
Maybe I am misunderstanding the chart the scope of its intent. I would refer it to you at any rate.
Now wouldn't it be neat if someone had access to live, non-faded, samples of any subject, and using color spectroscopy, compare the original colors with samples of paints. That would not be too hard would it...