I just wanted to save others from some disappointment - I had read online that you can develop color film (C41 or E6) in Black & White developer, and what you end up with is a B/W negative (or positive with E6 film!). There would be an overall color cast that can easily be removed in post, or kept if you like it.
So yesterday I took the 500C/M out for a little exercise. The only 120 film I had was Provia 100. I knew the results might be wonky, so I didn't take any photos that would be missed.
I developed the Provia in my usual FF No. 1 Monobath and..... nothing. I was expecting maybe very faint images, or low contrast or SOMEthing, but there was nothing. It just looked like undeveloped film.
So I suspect the Monobath is at fault. It probably doesn't have the right elements to clear off the color emulsion. I guess you need to use a normal B/W developer. Oh well. Lesson learned!
Next experiment (somewhere down the road) - developing C41 film in E6.