I'm not sure if anyone else has run into this, but the terrain color mode under the PRACX mod menu in game (Alt-T) seems broken. They will all show a mix of EGA colors (black, cyan, magenta, white) and brown. It's the same terrain on all the non normal options, except how much of the map is affected. It happens with both Terran_PRACX and Terranx_PRACX. I've tried a few comparability modes with no luck so far. This is under Windows 10.

OK, I found the fix already. I went to the PRACX Github and just downloaded the installer .exe file from releases. I had tried reinstalling the game from the GOG offline installer first, as well as rebooting my PC in case I hadn't since enabling DirectPlay, but those did not work.