I received the rebuild kit posted here last week from Muscle Car Research and upon cleaning the original hold off valve parts I noticed the round cover finish looks to be a gray phosphate type of finish. When dry it looks like the gray finish on my 45 ACP. In the images below you can see the interior gray finish as well as its extension into the flat machined edge. On the exterior you can clearly see the remaining gray finish in the machine mark rings. This leads me to believe the cover did in fact have a gray phosphate finish, at least in 67. I see many repro hold-offs and the cover cap is a gold cadmium color. Maybe that was later in 68-69 but this doesn't seem the case for '67. I have researched the CRG archives but can not find a definitive answer as to what the finish should be though I have seen another thread where another person with an early 68 Z had the same interior finish. Many say it was a bright zinc to gold finish. I'll be bringing pictures to shows in case the judging questions it.
Any other 67 or early 68 owners see the same on your hold-offs? If you haven't opened yours up yet, you may want to do it. It is a surprise of the amount of brown crud that develops inside though the outside looks clean.
Thanks to Muscle Car Research LLC for the fast delivery and excellent price!