I believe the caption that the "firewall" is usually unpainted in German aircraft is incorrect. Specific types and manufacturer may have had differences and very late-war production was often partly painted. However, much more common was RLM 02 (light grey-green) for interior painting. Certainly, WW2 Bf 109 production was painted RLM 02 on internal surfaces, including the engine bay. As said, very late production may have had major differences.
