Value returned is a reference to ImGearPageDisplay internal object. Accordingly, its modification affects parent ImGearPageDisplay.
For ImGearPresentationPageDisplay the value of IImGearBackground.IImGearBackground.Mode by default is ImGearBackgroundModes.NONE. To enable backgroud drawing for the ImGearPresentationPageDisplay, please set the IImGearBackground.IImGearBackground.Mode to ImGearBackgroundModes.BEYOND_IMAGE value.