Well, in the early years of the flathead the castings were painted after machining and before any assembly at all...there were masking fixtures for the gasket surfaces and such. See the "as Henry built it" book. I think it is likely that way was followed in later years.
This means all accessories and hardware were not painted with block, and gaskets were not painted either.
All the pulleys I come into contact with are sheet metal and were black...but this raises a question: Some late flathead crank pulleys are cast. Were those masked and painted at the foundry along with block and heads??