The monitor never ever changes the content inside the game lol. It's just how well it shows it as a picture.
I think it's the game itself that's messed up since it shows all the colours correctly and no signs of graphical glitches.
Save your files such as maps, objects and presets.
Go in the control panel and remove the game, then remove the folders.
Reinstall the game, and then it should work.
I'm rather certain you moved around the filed or renamed the textures, this causing it to load the same ground text everywhere.
If that doesn't work, uninstall it again and make sure you remove EVERYTHING.