[vtkusers] How to change the active cell attribute after "Render()"

[Jens]

Hi
Can anybody tell me how to change the active cell attribute after Render() got 
called.
I would like to let the user choose what cell-attribute he sees and therefor 
call:

	loadedGrid->GetCellData()->SetActiveScalars(newAtt);
	ren->Render();

but nothing happens. It is only possible to change the active attribute before 
I call Render() the first time.
I already tried
A)
	loadedGrid->GetCellData()->SetActiveScalars(newAtt);
	loadedGrid->Update();
	ren->Render();
B)
	loadedGrid->GetCellData()->SetActiveScalars(newAtt);
	loadedGrid->Modified();
	ren->Render();
C)
	loadedGrid->GetCellData()->SetActiveScalars(newAtt);
	loadedGrid->GetCellData()->Update();
	ren->Render();
D)
	loadedGrid->GetCellData()->SetActiveScalars(newAtt);
	loadedGrid->GetCellData()->Modified();
	ren->Render();

I´m using Vtk 5.0....
Anybody knows what I am doing wrong? Please tell me.

	Greetings
		Jens