unable to render QWidget on top of a QWindow

In the attached example application i create a QWindow (RasterWindow) and three QWidget objects (ColorWidget). I try to render the QWidgets on top of the QWindow, but the QWindow is always rendered on top of everything else.

I also tried using a QStackedLayout; put the QWindow on the bottom and the three QWidget objects on top, but on screen always the QWindow wins.