I've found the different color on the underlying paint in a trunk several times before.
I don't know the gun handling procedures they used regarding different colors, but I've wondered if they "sprayed out" a previous color in the trunk.
Also, were cars painted the same color done in batches? Or did they actually have guns for each color?... seems unlikely.

I've also seen a stripe of a contrasting color on the sail panel of a vinyl roof car. (Again, an underlying coat.) This one I had theorized could've been a reminder or sort of a "stop sign" to the painter not to paint the roof.
Interesting stuff that might not of been documented procedure or at least not I've seen in what I've looked at.

Ref: 1100mi. Camaro... I'd like to see that car after a couple days of careful cleanup. It looks like the car sat for years with a window or two open. If you look at the buckle tongue you can see how thick the dust is where it appears to have been disturbed. The pedals don't look worn as much as dirty... a short trip with muddy shoes?
Or was a burned out electric drill found on the bench next to the car?
We're all just speculating looking at pictures...
It would be a wonderful car to check out in person!

Rick