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BlueHeavenHero, I changed it to dirt, and now it looks like the Necropolis ground.
I made it in a mod by fktifzobr@mail.ru on the previous page.
In the DirtArena01 file, I substituted the values in AmbientColor with those from RP1_GrassArena01(VicTest) (for Haven). The skeletons and background became less green. You can also play around with LightColor there.