I've read dozens of posts on the subject of Pz Gray being used as a last resort cammo. But.. The "conventional wisdom" is that this just didn't happen.
If I were to build a speculative "final days" Pz 4, 5, 6 or variants, I'd go overall primer red with thin hard edge dark green and Pz Gray cammo... I could invision the factories making do with a quick, spartan, cammo scheme over the primer using whatever paint stocks were at hand. But then, I'm not a a bolt-counter. JMHO!