On FB our own lonepigeon IDed them as the same round switch covers as used on TIE chest boxes, but in black. He thinks they were inherintenly black, not painted, which would make them semi-transluscent, I guess.
They don't seem translucent. A couple of them are still intact on the helmet in the archives.
Maybe similar to the white ones on the TIE chest box that also look opaque. Sometimes there are both light up and solid versions of push buttons.
RS didn't sell round ones, at least at the time, so they must have gotten them from another supplier.
On FB our own lonepigeon IDed them as the same round switch covers as used on TIE chest boxes, but in black. He thinks they were inherintenly black, not painted, which would make them semi-transluscent, I guess.