Well, since this can of worms is open...
1) The FS system didn't exist until after the war, so remember that any use of FS to refer to a WW II color is an approximation and not THE color per some government spec.
2) The ANA system was not implemented until after the US entered the war as a way to standardize paint production in the US, the UK MAP agreed to use it however by the time it was fully implemented it was about the same time the USAAF was switching to NMF. Both date to after the P-40B/C Tomahawks were being delivered.
3) The MAP contracted with US manufacturers for aircraft to be painted to their specs, not to something else like some modelers believe (the "there's a war on, you know" theory).
4) The MAP specs basically required paint to be the same Dark Earth, Dark Green and Sky colors that were being applied on UK manufactured aircraft (not the same paint, but US made paints that were the same colors and to the same durability requirements). To help clarify, the MAP identified specific Dupont paints as being an equivalent to the MAP specified colors. The "close enough for government work" statements that are the source of most of the controversy. There is actually a color chip card approved by the MAP here.
5) The Dupont equivalents to the Air Ministry (AM) colors were:
- AM Dark Earth -- 71-065 Dark Earth (a very close match)
- AM Dark Green -- 71-013 Dark Green (slightly bluer than AM Dark Green)
- AM Sky -- 71-021 Sky Gray (lighter and a hint bluer than AM Sky, but it's not gray)
The controversy is mainly with 71-021. Contemporary color photos make the light color look more bluish gray than it really is (okay that's my opinion) so some modelers content it's really a bluish gray color like x6622.
There is some controversy over 71-013 Dark Green. Generally most modelers agree x34092 is a close match to 71-013 Dark Green.
There is generally no controversy over Dark Earth, however some believe 71-009 Dark Earth (yes, Dupont used the same name!) which is a lighter color, closer to a Sand color, was used on some production batches.
I've chased AVG P-40 colors for a number of decades, trying to get a model to look right. I finally settled on:
- Dark Earth -- any favorite RAF Dark Earth -- I use Humbrol 29
- Dark Green -- Model Master 1764 European Dark Green FS34092
- Sky -- Gunze H314 35622 (too blue, still not quite to my liking but close)
Read this blog, it's very informative and written by a well respected Brit who knows and understands color. It was written well after the IPMS Stockholm reference charts which can be outdated.
Ultimately I hope you paint it to your standards, it's your model and it should look the way you want it to.
Tim