When the cable outside the housing turns black it is easy to tell that it is not SS

I can certainly tell when installing them. I used to solder the ends of galvanized cables to keep them from unraveling. I had a lot of troubles getting the solder to stick to stainless cables so I moved to TIG welding the ends.

In use, I had issues with cables/housings rusting. And, rust at the over the bottom bracket cable guides.

The color of the cables is slightly different too. The galvanized cables are greyer, and the stainless cables are shiny.

I did accidentally get a batch of galvanized shifter cables, I think, that I ordered from China expecting stainless. I could try to track them down and check the condition and ship them somewhere.

I have NOS galvanized cables with the Huret disc end. PM if you're interested and we can work something out. Otherwise, you can make your own Huret-compatible stainless cables by squeezing the barrel of a modern cable in a vise until it fits the slot in the lever. Some minor touch-up with a file may be necessary, but nothing too onerous.

Thanks for the offer John. I bought a few of these from Ben's.
https://www.benscycle.com/jagwire-ba...-1265-ca6555/p

I currently have a project on hand which needs blue cable housing, which I found today at a jumble in Belgium:

https://cimg8.ibsrv.net/gimg/bikefor...6caadd096d.jpg

It is not lined, so I was happy to find these galvanize cable sets as well. And at €1 a set, I thought I might as well grab a handful.

https://cimg6.ibsrv.net/gimg/bikefor...955bbfe8c0.jpg