You can start with this https://www.ageofempires.com/mods/details/1592/
Oh, and the Lunar New Year event also had a night themed main menu background https://www.ageofempires.com/mods/details/3340/
And then ask @WanMonstar how’s their night theme color correction mod is going on xD I’m trapped: colorcorrection_json doesn’t work?