PopUpManager places a full-screen display object behind the popup. You can specify its transparency and amount of blur via styles.
The window should be available as systemManager.popupChildren.getChildAt(0)
Then you could try messing with it to change its position and other visuals.
But for me the PopupManager doesn't place the overlay for the full screen (i.e., parent of that popup).
In my situation, am having a shell window which has swfloader as child (this is placed in some XY coordination only, not entire screen). Application movies will be loaded into swfloader dynamically. The loaded application has popup screen. Now when the popup screen launched, the overlay has been positioned as X and Y as 0, but its parent window is placed at Y = 54, which results the overlay has not set on the entire window, it sets upto some height only (the height of parent application screen).
I want to show the overlay entire screen behind the pop-up window. How to achieve this?