I came back to this game on a whim and found the 1.4 version straight off of GOG has an issue where the map is entirely dark other than one diagonal ray of light. Searching up the issue I found about the fan 1.5 patch that fixes that as well as other things, but under 1.5 the ground is really luminous and it frankly looks much worse than 1.4. Changing the game's video settings didn't help.
Looking at how the map displays in 1.5, with ugly bright terrain against the dark background I'm wondering if this is an intentional/blunt fix to get the map working, but is there any way to fix/disable this? I'd like to keep the general graphic improvements of 1.5 (the water looks so much nicer), but without everything being so egregiously luminous.

The brighter version is how the game is supposed to look. The crushed dark terrain is an issue with Nvidia cards when they do the landscape bump map shader.

I deliberately enable the brighter version without using > 1.4 patches because I run it on my retro XP machine and the newer patches don't work on XP.

To enable it:
Copy the *.pso and *.vso files out of the patch 1.497 or 1.5 patches. Use 7zip to extract the contents of the patch .exe if needed. Drop them in the game folder.

To disable it:
Delete all the *.pso and *.vso files in the game folder

You might want to play around with keeping some of the *.pso or *.vso files, maybe you only need to delete the landscape.* or bumpmodel.* files to get the look you want. You may also need to tinker with swapping the gg_dx7r.dll from the patch vs renaming the patch copy of gg_dx8r.dll to gg_dx7r.dll, or using the original from the gog install.