[OG68]

Or natural cast.
It seems that they came painted or unpainted. You'll find original owners that will say their original Master Cylinder was painted / not painted.
I wondered if it was an assembly plant thing, but in my own case, to the best of my memory, my Fremont 68 MC came unpainted, while others tell me their Fremont cars MCs were painted.

Same discussion over on the Chevelle forum. Speculation is that Delco Moraine had several plants building MCs. Some shipped them painted, others didn't.

Who has a definitive answer? Original owners with original MCs. See above ...

So I think both ways are correct.