Hi Steve,
The early "Camoutint" was a green tint, yes. It took many, many hours of research to dig that out mind you.
Almost everyone thought it was, as you used here, close to the colour of the prototype. There were some dissenters. I vascillated between the two beliefs to be honest. But I eventually found a professional model that Shorty Longbottom had commissioned by Woodason (who did recognition models for the RAF. From memory he paid them 5 quid... a not inconsiderable sum!!!
Given the company that made the model and the source of the commission, I'd be certain that this is the actual colour that N3071 was painted (and her sister ship N3069). It is more than likely that the source of the paint on teh model was RAF stores. It is the colour that Cotton's medium altitude Electra was painted before the war. In all probability, N3069 and N3071 were the only Spitfires to be painted as such. The Blenheims used early on were also this colour.
A little later the light blue (as you did here) was used and then the more familiar mid to late war PRU Blue (as you did for me on K9817) was adopted once it became obvious that at high altitude the lighter colours stood out rather than helped.
Cheers
D