[Graham Boak]

I dug out the magazine, and the reference to the blue is not in the article by Paul Lucas, but in the model build by Neil Robinson. It states that "there is a distinct probability that by May 1940, some of 1 Sq machines had their undersurfaces painted a "pale blue" colour. ..the date..rather vague...the shade...even vaguer." The origin or credibility of this imprecise information is not given.

The magazine also has three examples of black/white undersides, with serials straddling G.

How about going way back to the source? The first aircraft book I bought was the very Fighter Pilot, by Paul Richey, and I still have it. There are two helpful photos. One if G itself after losing its prop. Only the nose is shown, and the underside is in shadow, but certainly appears dark rather than light or reflective. The other is a photo of T showing the underside (specifically, clearly, the radiator) split into white and black. The underside of the rear fuselage is dark except for the area around the tailwheel, which appears to be a replacement in Aluminium or White.

So I think the black/white undersides with roundels on G is fairly well established, at least up until April if not until the end on the 11th May.

I don't know when the squadron stopped using the JX codes, but well before May.