What everyone else said, with the addition that I understand
(at least in North American's case, probably the other US manufacturer's
as well), they used whatever color they had on hand at the time the
details were being fabricated / painted. Both colors were allowable
per the spec(s). Had a bunch of yellow ZC on hand? That was sprayed.
Bunch of green? Have at it.
Tends to drive restorers nuts when they have documented "survivor"
examples to go from only to find another documented / survivor
airframe that differed here and there. Bottom line, there was a war
going on and nobody was particularly concerned with having the
detail components of the airplane(s) all one color <grins>.
To draw an analogy, in the car restoration circles (I'm particularly
familiar with Corvettes), folks argue long and hard about what
the factory did 30, 40 or more years ago. The quick answer is
they did whatever they had to that day to get the cars out of
the plant and on the way to the dealers to be sold....
I've purchased and installed numerous "NOS" parts on my SNJ
from well known parts suppliers. Some had the lightest coat
of green ZC on them you've ever seen. Some had primer
applied so heavily that stripping the part of paint halved the
weight of it. Some were sprayed with yellow ZC (some heavy,
some light).
There's a picture in some recently published book of a (relatively)
young man spray painting (priming?) Bell P-39 cockpit door assemblies.
He has a funny look on his face, and is wearing no protection
what-so-ever (no respirator). Perhaps that points us towards a
possible answer as to why and how WW-II aircraft detail parts
were originally primed/painted the way they were. Everyone
involved was high on toxic paint fumes!
