Protocol for low rate data over a single wire

[dfmischler]

Is this really the case when the connectors are not mains types?

Yes - IEC61010-1 has a clause that goes "green or green / yellow wires not used for any purpose other than safety earth". I had to reject a design for breaking that very clause a few years ago.

How do you reconcile this with, say, ISO/IEC 11801:1995 referring to the EIA/TIA 568 color schemes (in which green is half of a data pair)?