Surprised someone didn't pop in with the answer bcm. I'm personally not 100% sure myself, but always thought it was related to "polyurethane" which was/is a family of paints. But "poly" is generically used for many plastics and such, so at the time someone may have given the name to some colors that sort of looked like a plastic coating. Or since it really means "many" I think, maybe it's just from a joining of multiple existing colors to reach a new one? Long shot too, since pretty much any color that's not a prime color is a "mix of colors" so not sure how far that theory goes.
That's a very long stretch, and I'm more inclined to think it was short for polyurethane, but I'll just bring this back to the top so some of the older painters, or older Ford guys in the group can answer.
In the meantime, what is the color for paint code "D" in '68?
I'm going to go through the thread again, but in case someone can answer that quicker, that would be great.
Thanks
Paul