I think the color picture you posted of “The Miami Clipper” shows exactly what you want. I think it is zinc chromate yellow showing up on the leading edge of the wing.

I have a color picture of a Vought F4U in one of my book by Dana Bell that shows something similar. The paint was worn off by coral dust and prop wash. It shows the ZC on the leading edge of the wing and stabilizer.

It’s very possible that the camouflage planes were primed with ZC prior to painting. It makes sense that the Natural Metal ones were left as is.

The pictures I posted show a few camouflage planes with bare metal surface underneath.

It’s most likely a combination of these things and could have been a variation depending upon which factory and even what time era the planes were built.

Like I mentioned before, anything is possible.

Jay, just my 2 cents from an aircraft mechanic's point of view - since deicer boots are inflatable devices, they are normally glued to the leading edge of the wing with rubber contact cement. Screws aren't used because the boots have to be airtight. Whenever I've installed them, the paint is stripped from the leading edge so the glue has something solid to stick to. Having said that, when push comes to shove, anything goes, so it's entirely possible the leading edges were primered before the boots were installed, especially on earlier production airplanes. But, it could also be glue residue, which is a yellowish color. Best recourse there is reference photos of the specific airplane you're modeling.

And, of course, all bets are off once the airplane gets into the field!