Assuming it can't be related to what I'm running into. Can degaussing CRT glitch VGA signals?

About killing the Explorer process, did you do that prior to running a game which uses the 256 color mode?

There is also some workarounds at PCGamingWiki related to the 256 color mode, I know that your problem is not with rainbow colors but perhaps you can try some of these such as the registry hack.

Gmlb256 wrote on 2021-08-14, 18:27:

About killing the Explorer process, did you do that prior to running a game which uses the 256 color mode?

I've typically killed the explorer after the game launches with a .bat file and delays, but I've tried both ways without any effect on the black & white issue.

Gmlb256 wrote on 2021-08-14, 18:27:

There is also some workarounds at PCGamingWiki related to the 256 color mode, I know that your problem is not with rainbow colors but perhaps you can try some of these such as the registry hack.

That has been a great resource. I've used all of them except Display Changer II , I've found it to be just a bit daunting to get configured. Some solutions that get games out of 256-color mode work, anything that tries to simply correct color palette issues leaves me with black & white.

I fear that I caused the issue at some point with an attempted fix that I have since lost track of and therefor don't know how to reverse. I could just start over again with a fresh install of Win 7, it just hurts a bit as I have gotten over 600 old CD-based games working thru various tweaks and patches that in my haste I didn't document perfectly.

Some third-party utilities may cause issues in the long run. When Windows 7 was mainstream, I previously used Driver Sweeper when I was using a ATI/AMD graphics card on my main computer and one of these versions deleted some essentials files which prevented me to install the Service Pack 1 for Windows 7.

Had to reinstall the OS to address that one.

256 color mode was broken in Windows 7. I was never able to make it work without glitches.
In Windows 10 the problem seems to be fixed.

Azarien wrote on 2021-08-14, 23:11:

256 color mode was broken in Windows 7. I was never able to make it work without glitches.

For me the 256 color mode in Windows 7 worked when killing the Explorer process and/or using the registry trick on a program that uses it in fullscreen mode. I tested that on the original Age of Empires and Hellbender in software rendering mode.

I haven't run 256 color mode in a while on Windows 7 but the last time I did disabling Aero did the trick. It was a lapop with AMD HD6310 GPU.