contentBackgroundAlpha has no effect on AdvancedDataGrid

I am trying to make the AdvancedDataGrid blend into the backg开发者_StackOverflowround by setting contentBackgroundAlpha=0. It doesn't do anything. How come?

Set the alternating item colors to an empty array.

<mx:DataGrid contentBackgroundAlpha="0"
             alternatingItemColors="[]">
    <mx:dataProvider>
        <mx:ArrayList>
            <mx:source>
                <fx:Object data="1" />
                <fx:Object data="2" />
                <fx:Object data="3" />
                <fx:Object data="4" />
                <fx:Object data="5" />
                <fx:Object data="6" />
                <fx:Object data="7" />
                <fx:Object data="8" />
                <fx:Object data="9" />
            </mx:source>
        </mx:ArrayList>
    </mx:dataProvider>
</mx:DataGrid>