Seriously , it's referred to as grey-green and to my eyes it looks as Airframes described it above, a greyish green.
That's the problem though, colour perception is not objective. An expert could post all sorts of scientific values (Munsell) to tell us whether it is yellow, green or whatever, and be completely objective. Unfortunately that might not be what are eyes and brains perceive.
I'd say the photo of the area behind the Spitfire seat, posted above, gives a pretty good idea of the sort of colour you're after. Anything in that ball park, on a model, will look fine.