Jack: Yeah, I don't know if Sailor had much clout after Barking Creek, until he had a chance to redeem himself.
I have Paul Lucas' book on RAF camouflage and markings through the Battle of Britain, and he goes into great detail about the various paint schemes used before the war and in the early days of the war. It's an interesting read; very informative.
One issue I had, though, was the matter of underwing roundels. According to Lucas, underwing roundels were applied to day fighters as of 4 June, 1940--the end of the Dunkirk evacuation. Prior to that, RAF fighters over Dunkirk should presumably not be carrying them.
Yet, here's a photo I found, purportedly showing a downed Spitfire from the time of Operation Dynamo.
Then, to complicate things, Lucas says that only two days later--on 6 June, 1940--Sky, Type S was ordered for the undersurfaces, and the underwing roundels were once again removed until 11 August (p. 33 in Camouflage & Markings, No. 2).
I opted to leave the roundels off the bottom of the wings on Sailor's plane, since Revell's painting instructions didn't show them and their decal sheet didn't provide them; but the issue is something I haven't figured out yet.
Caspar's old decal sheet for Operation Dynamo shows underwing roundels on both Spitfires and the Hurricane included in the set. Still photos from the upcoming Dunkirk movie show roundels, too, on the wing bottoms.