Thanks for the extra work, hang-single.
I checked everything I could see in the interface, and nothing is left out on your side from what is visible. I typically ask for a file, as images and videos leave me guessing pretty much constantly. But here, I felt it might be more a limitation or hardware driven. Hardware things are not something I can simulate here for the innumerable combinations that are possible.
What I couldn't see what your color management settings.
I get different results here (I'm on Mac, and I have a different graphic card.), but I also have no option with Redshift while using RS materials.
The Standard material works fine. However, if I switch the color management, it also changes here. This needs more technical attention, which I'm not supposed to provide here; that is the tech support area.
I have tested it with all materials in the scene or only one each time.
To have the same texture in two instances while painting in one might create problems when saving the texture.
Since the Help Content is not limiting the use to Standard Render only, Please have a chat with tech support:
https://www.maxon.net/en/support-center
Thanks again for all the effort. I will file my report here. Perhaps you will hear that it is known, and that could be based on your input and my follow-up report.
My best wishes.
