Plastic Color Restoration
What is fascinating to me is that I have no good reference for what the plastic looked like 45 years ago. When exposed to UV, plastic will change color. Same goes for solvent rich fumes (gas tank in the same trunk cavity as the tool kit). Question is, do any of us actually know what the plastic looked like off the showroom floor? Even within a collection of perfect references, were there different suppliers and/or different formulations and batches that offered slight variation over the years? I'd guess yes.
Based on the (2) donor shells I have, I am making an assumption that the one that is clearly not as faded and yellowed is more accurate. And within that reference, the top surface of the upper shell - the part that was against the deck lid and should have seen no UV exposure - is likely the closest reference I have.
I have made mock-up color tests with SEM Color Coat aerosol: Storm Gray and Warm Gray (as suggested by others on the forum). At first glance (on the still dirty/not well cleaned donor lid), the Storm Gray is a closer match in overall tone. Which is to say, the Warm Gray looks lighter. But in person here, we can see that the Storm Gray almost has a hint of blue/red (yes, sort of purple). Just a slight hue. Might not be noticeable if it weren't being compared to the other adjacent plastic.
But when compared to the back of the "good" reference piece, I think the Warm Gray is a more accurate match to my "as close to the original as I have available". With that in mind, I think I'll go with the Warm Gray for the final piece.
My "good" cover piece is currently clamped up with some epoxy setting up in two hairline cracks. After that is complete, I will begin to restore some other areas that are missing.