I've run into a slight problem that I am not seeing the answer to. I'm trying to apply a mask (a canvas) to another canvas. But for some reason the mask is not doing it's job.

Below is my code:
Code:
	<mx:Canvas id="masker" 
		width="300" height="400"
		visible="false" backgroundColor="#000000" />
		
	<mx:Canvas id="target"
		width="400" height="700"
		mask="{masker}"
		backgroundColor="#FF0000">
		<mx:Canvas backgroundColor="#00FF00"
			width="50%" height="50%"
			right="0" bottom="0" />
		<mx:Canvas backgroundColor="#00FF00"
			width="50%" height="50%"  x="0" y="0"/>
	</mx:Canvas>
Any help on this would be greatly appreciated.