IIRC, Zinc Chromate was basically used as a base for anti-corrosion finish, used on the interior of some aircraft during WWII (AFAIK, the B-17 and B-24 were not among these, but I could be wrong); as has been mentioned, the actual tone varied due to allowed formulaic variation as exact specs in wartime can run afoul of shortages! Allowing for shortages of given materials in wartime meant one could always get the finish, else one would be "dead in the water!" IIRC, "Interior Green" started as a nickname bestowed by aircrews for the zinc-chromate-based finishes, and some time post-war the U.S. military gave an actual color-spec to the name "Interior Green" . I suspect the Testor color might be to this post-war spec, and since anything I make that would need the color would be from WWII, I mix my own too, and even add a drop of black for the "lamp-black!"
Regards, John