Nice work Peter, and I agree, the cockpit colour looks good enough to me.
Although it's an 'early' Spit, it's in the 'X' serial range, so not that early, so the colour is more than likely correct, or as near as dammit for the scale. As far as I know, it was the very early Spits which were lighter in colour, and then only by a 'shade' or so, I believe.
The oldest Spitfire in existence is the Mk1, K9942, in the RAFM, Cosford. Although it's difficult to assess properly in the photo below, the green colour can be seen behind the seat, and although it is lighter than what became the 'standard' grey-green, in 'real life', when viewing it in the Museum, it's not that far removed, and would only really be noticeable if compared side-by-side.
I'm really hacked-off that the Museum is having their next 'Open Cockpits' nights on the same weekend as the BoB 75th airshow at Duxford, so I can't go - and K9942 is one of the aircraft being opened-up for viewing, although understandably, it's viewing only, no sitting in this one !