I found this very interesting article on Japanese primer colours found on a A6M3 Model 32 Zero in 1942. Not one but four different primer colours on the one aircraft!

http://colesaircraft.blogspot.com.au/2014/01/japanese-wwii-aircraft-aotake-primer.html

It shows a great colour photo that sums it all up to me ...if it looks right then it is right! Modelling is about fun. No need to get hung up about convention on what it should be, there will always a photo to show otherwise.....