[2020] yellow gradient

If you're thinking of what I'm thinking of, then it's the ruined texture. The best option I've found is to find a map theme that was a very subtle ruined texture or has one that's just grass. You can use the Theme Mixer 2 mod to easily try out themes in game. Then it's just subscribing to a bunch and seeing which one(s) you like best.

This theme is one I know uses a grass texture for the ruined one, so it simply isn't visible.
https://steamcommunity.com/sharedfiles/filedetails/?id=774725900