<mx:Canvas id="maincanvas" backgroundColor="7000" width="100%" height="100%">
<mx:TextArea backgroundAlpha="0"/>
</mx:Canvas>
However if I try creating a new textarea object via:
var textarea:TextArea = new TextArea ();
textarea.backgroundAlpha = 0;
maincanvas.addChild(textarea);
flex throws the error :
1119: Access of possibly undefined property backgroundAlpha through a reference with static type mx.controls:TextArea.