There could be at most three [!:Autodesk::Revit::DB::ColorFillScheme] applied in a view: one for spatial elements (rooms, zones, spaces and areas), one for pipes and one for ducts.
Notes:
There’s at most one scheme activated for all spatial categories.
For area plan view, the activated spatial scheme category must be OST_Areas and has the same [!:Autodesk::Revit::DB::AreaScheme] with this view if it is not used as a template.
To clear one of the above three schemes, use InvalidElementId as the parameter of this function.