Removing layers of paint.

[Schonyenko2]

What exactly are you trying to determine? The original color, or a clue of what the car spent part of it's existence as. ie: race car, custom show car, ?.
First what brand is it, and what year? That will help as different mfg's used different sub coats. It's also difficult to know as there appears to be cut throughs to bare matal from previous pnt jobs.
My Guess is that it appears to be a GM with the usual black primer, with a grey sealer, and was originally white. The rest is up for grabs.

Joe, I can find the meadow, but where's the naked ladies.