Thanks Dave, That is certainly a more sophisticated analysis of the paint layers than I was aware of.
I think it discounts the suggestion of a complete paint strip in the 70s.
Without a chemical analysis of the red paint layer, it is still open whether it was a primer or a colour layer... but it certainly could be a crimson lake top coat.
Jenkins, in 'Railway Archive', notes his assumptions that on arrival at Wantage it was probably LNWR black, then GWR green, then 'during the Edwardian period it apparently was painted crimson lake.'
The somewhat haphazard repaint policy noted by Higgins leaves it open whether all locos were so treated, but the case for the red colour for Jane looks stronger
C.Man.Micheal, in British Railways Illustrated, includes a photo of Tram Loco No 6, with the caption 'the engine is wearing the official WTC livery of GWR-style green, and the car is green and buff'.
This was in about 1920... around the time that the two steam locos were in and out of Swindon works.
In the absence of any evidence to the contrary, I'm happy to take both these claims at face value.
Returning to Mike's project... he is of course free to paint it as he wishes, and unless he is portraying that particular loco at a specific time in the line's history, no one can say it's incorrect.
My own Wantage project is set in 1923, for a variety of reasons, including photo references, track changes, minor car livery changes etc... and it's right in the middle of the Swindon connections; so I am confident in my choice of what C.Man.Micheal calls the 'official WTC livery' at that time... whilst being more open than I was before, to the possibility of an earlier, different livery.
That's why we come here... to learn stuff !
Cheers, Overseer, Dave, and Mike.