Reviving this thread to pose a question.
I have suspected, ever since discovering the "AT-6B" I'm working on has a Harvard Mk4 steel frame, that the fuselage frame is also Harvard Mk4. Circumstantial evidence was the presence of Mk4 finishing strips in both front and rear cockpits.
This weekend, I had to remove the lower attachment rail for the left side fuse side panel to remove a bunch of drilled out blind nuts. When I got the rail in the shop, I noticed the bottom of the rail was a decidedly lighter color green than the green zinc chromate. With the fuse side panel on, painting the inside of the fuselage area would have required a contortionist to reach down to paint the underside of the rail, which wouldn't be seen anyway.
So, I am reasoning, the light, almost pastel bluish-green paint might even be the original interior color. I wish I had taken a picture to post and may do so next weekend. Until then, working from memory, I made these paint swatches.

Which brings me to a question for the Harvard guys out there with Mk4 insights. What was the original interior color of the Mk4s built for the RCAF? Anything like the "mystery color" swatch?
I've seen a few Harvard cockpit pics with a bluish (turquoise) paint, but most are restorations and have the green chromate, or grey interior.
Thoughts and ideas appreciated.
Thanks!