Setting background-color for Flex Tree component..?

I have a Flex Tree component in my app. I set the icons for open and close. BUT 开发者_如何转开发I can't find something about changing the default background-color from white to something different.

obviously there is no background-color setable in css...

any ideas?

thank you

myTree.setStyle( "backgroundColor", 0xFF66600 );

or

backgroundColor="blue"