code: def setOverlayRenderModel(self, ulOverlayHandle, pchRenderModel):
          
  
          fn = self.function_table.setOverlayRenderModel
          pColor = HmdColor_t()
          result = fn(ulOverlayHandle, pchRenderModel, byref(pColor))
          return result, pColor
docs: Sets render model to draw behind this overlay and the vertex color to use, pass null for pColor to match the overlays vertex color. 
          The model is scaled by the same amount as the overlay, with a default of 1m.