Interesting original paint oddity.

[hewittca]

Hi all. I recently purchased my first c10 and it is basically all original except for the wheels. It's still wearing its original dark green paint with turquoise column, belts, and visors. It has typical patina everywhere (red oxide primer on cab and black everywhere else, see door jam pic), EXCEPT for on the firewall. I was doing some work on the motor today and noticed that there is a spot of dark green missing and beneath it is turquoise!? I thought that maybe some paint got transferred to it at some point, so I sanded a bit of the green off and sure enough there is turquoise beneath it. I don't know anything about how these trucks were painted on the assembly line, but I have never seen this before. The section of firewall in question does appear to be part of the cab and not a bolted on piece. The firewall does also still have the original chalk marks. I'm stumped, any paint gurus out there that could share some insight?