Variation does exist on automotive paint.
I don't think it's usually that large.
No idea on an FGT.
I think the measuring devices are often magnets....which normally don't work with aluminum.
Some of the paint gauges do work on aluminum.
Regarding what NorthwoodGT said,..if you do an oil change and look around you will see your VIN stamped on the frame. Certainly something you wanna see.