Obviously, impossible to say for sure from the photograph Rod, but I don't really see "yellow" in that top/central Victor. So no, it does not appear to be a standard color for this casting. The first thing that came to mind for me was that the color looked like the cream or pinkish-cream used on the 74A Refreshment canteens and the early 22B Vauxhall Cresta models.
The Victor joined the range (according to Stannard) sometime in 1958. The model we're talking about appears to be a green windowed example with 9mm GPW. Not a model from early in the model's life within the range.
The 22B Cresta also joined the range in 1958.
The Refreshment canteen joined the range in November of 1959. I suppose it is conceivable that the Victor in question could have gone through the line around the same time they were painting the early cream, pinkish-cream canteens and Crestas.
But then this is the red-green color blind guy offering up input here, so take everything I offer with a healthy dose of skepticism.
