Topic on Skin talk:Citizen

Theme color can be set using $wgCitizenThemeDefault

With auto, it's very hard to author for. Even if I create light and dark versions of background images (for example), when it's set to auto, I'm not able to set the correct one. Resulting in broken designs (and my only option being to disable these nice additions in auto all-together)

Are you looking for $wgCitizenThemeDefault? This can be set to either dark or light