As pointed out the headliner would be black in a Plymouth Gran Coupe
The standard interior code should be PRXW which is white leather. The door panels would be white with Gran Coupe emblems in them
Just got to the fender tag again. The code is PRXW. So this car had white leather seats.
I've posted a shot of the headliner too. At a closer look, it sure does not appear original to me? It is vinyl.
Also a shot of the drivers seat in it. Not original either, obviously. So it appears this car on the inside has had work done down thru the years after all.