My recollection was that I had only ever noticed the black switches to have "clear" bright zinc, and the red switches to have the yellow passivate finish.
So, I just looked at my NOS switches which appear to confirm the red switches to have a distinct yellow/gold appearance to the zinc.
However, the one NOS black switch I have has a definite light yellow tint to it, though much less so than the NOS red switch. This switch is of course in very old packaging and has been stored hidden away in a box for the last 25 years that I know of. Suggests to me that black finish switches may not all of been clear (ie bright silver) zinc. Or maybe the originals I have that appear to be just clear zinc were originally slightly yellow in appearance and have age faded. Personally I think I would choose to go for clear zinc rather than yellow if I were to restore an old switch.
Anyone got any good detail pictures of a VW restoration to check out?
Chris R.