You are not going to like my answer. Unfortunately zinc chromate is a misnomer. It is not an actual colour. Zinc chromate is a protective coating with pigment. This comes in all sorts of different shades ranging from an almost lime green to mustard yellow and probably many others. You’re either going to a) choose a colour you prefer or think is appropriate, or do some research to find out what plane where it was made and what pigments they might’ve been using. During this war time effort things changed rapidly and many colours were improvised.