I have a 70 Cuda Vert FC7 built at Hamtramck. It has remanace signs of having the gray, red oxide and black.
Any ideas of what it shoud be?

Which color is closet to the bare metal, as it been restored in the past ?

Hasn't been restored before. Not undercoated no gray on the bottom mostly dirt and something that might have been faded black. I couldn't figure if it was really cheap paint or a mix of oil and dirt. It had the gray dip on the inside with red oxide on top of that and then color
The car sat in a Texas wrecking yard for awhile.

Bottom body dip color should also match whatever is found inside behind the door panels etc. Used car dealer, or a past owner, may have sprayed something else on the bottom at some point? I would use whatever shade of grey or black you find inside the car.

Grey bottom, Red Oxide on top. Troy's T/A looked like faint rust on top, but it was the worn thin faded paint showing the red oxide underneath. Built at Hamtramck in the T/A-AAR period like your AAR.

Seems to really show on Silver cars for some reason

Black you are seeing may be overspray from wheel wells, truck black out, pinch weld black out (sometimes sprayed).

LA cars seems to have black primer/base on underneath.

That works the Vert had the same red on the top
Thanks