[Nicholas]

Tricky one - a veritable can of worms. I thought you would be flooded with replies on this!

Upper surfaces: Du Pont DUCO 71-013 Dark Green - close to FS 34092, Methuen 25-26 F 5, Pantone 553U. Du Pont DUCO 71-009 Dark Earth - close to FS 30219, Methuen 6 D 5-4, Pantone 4635U-4645U. This colour is frequently referred to as "sandy earth". Du Pont also used another, darker 'Dark Earth' - 71-065, closer to 30118, associated with desert schemes but it may have been used later in the P-40E production run resulting in a lower contrast upper scheme.

Under surfaces: Curtiss were initially confused by references to 'Sky'. There were at least three identified undersurface colours: Aircraft Gray, a pale gray close to FS 36473 and believed to be the intended match for RAF Sky Grey. Pastel blue, probably based on the Spec 14057 colour #27 Light Blue - a slightly greener version of FS 35526 or a lighter, bluer version of FS 35414, believed to be the intended match for RAF Sky Blue. Neutral Gray - possibly an anomalous, expedient colour.

For specifics: ET603 (Star Dust) undersurfaces probably Neutral Gray; ET604 (wreck examined by Geoff Pentland) probably Pastel Blue (described as "darker and stronger than Sky Blue" with a greenish caste - may even have been a deteriorated Azure Blue. ET615 (Scatterbrain) probably Aircraft Gray (Sky Grey).

Bear in mind that supply demands could and did result in paint batch variations and the use of expedient colours. The demands on Curtiss at this time meant that production could not be held up because paint of the exact colour was not available.

This is a summarised response. The subject of P-40 camouflage deserves a detailed and definitive study in its own right.