Body color written on firewall - "RGRN" for Rally Green here. 10A build.
I believe interior paint color was written on the passenger side rear seat bulkead (on at least early norwood cars). "LG" for light green interor paint (officially "Medium Green"). Fisher needed an easy way to know what color to paint inside and outside on the back half of the car.
Was the RGRN on the firewall blackout on under it?
I can't say for certain either way. I did not find firewall marking until my car was apart. Maybe 23 years ago or so. Owned it over 40 years so no resto grafitti. I did spray bomb the firewall black at that time.
Found a few inspection marks (not all 3) on the side of the firewall (behind the front fenders once they were off).
Rear bulkhead marks were yellow, very dry, almost chalky. Some of it rubbed off when touched. Found that marking back about 1979. "LG7"