Two overlapping vtkPolyData render flashes

Hi everybody,
I would like to render two overlapping vtkPolyData using two different color(white and yellow) maps in the same renderer. i want to show yellow vtkPolyData. but, The result is as shown in the figure. what should i do.result

Search for “coincident topology” in the VTK documentation to find methods to force one mesh appear in front of the other when they are very close.