vtkCompositePolyDataMapper2 renders objects darker compared to vtkPolyDataMapper
A script (compare_mappers.py) that compares the result of rendering a sphere with vtkPolyDataMapper, vtkCompositePolyDataMapper and vtkCompositePolyDataMapper2 shows that the latter renders objects significantly darker than the first two.
Note that the result for vtkCompositePolyDataMapper (the middle renderers) are only as shown if the vtkCompositePolyDataMapper::MakeAMapper method shallow-copies the properties from itself into the delegate vtkPolyDataMapper. I will add a separate contribution that realizes this.