Background Main Color (pre-v5.9: Background color). Specifies the background colour to be used for Map views and all other view windows — i.e. all windows except Note windows and Tinderbox dialogs/palettes. Inherited by the $MapBackgroundColor attribute. Default colour value is #f2f2e6.
From v5.9.0 this also sets the primary colour for map background patterns (in Map view only - not other main views).