I'm working on numerous projects at the same time and wondering about factory applied German colors. Was Zimm applies after the red oxide primer, then the base color? or was red oxide applies over Zimm? Hard to find reference pics regarding this application. Most of the pictures I can find don't show factory applied zimm during the application process.
Any help would be appeciated.

AFAIK, the red primer was applied as anti-rust protection. Therefore, it definitely would be applied onto the metal, not onto the Zimm (consisting more or less of cement). So the correct order for the time frame you're going for (factory-applied Zimm, i.e. roughly Septembre 1943 - Septembre 1944) would be

- metal
- red primer
- zimm
- base colour
- camo pattern in dunkelgrün and/ or schokoladenbraun

Thank you. I was on the right track. after looking at the photos of restored tanks it is hard to determine. And old factory images is hard to determine the actual color.

FWIW, I agree with Nicholas' sequence.

One thing to note is that Zimmerit was pre-colored with yellow ocher pigment as part of its formula, so it had some effect on the final factory Dark Yellow base coat.