The following example shows how you can change the background color and alpha of a PopUpButton control’s pop up menu in Flex by setting the popUpStyleName, backgroundAlpha, and backgroundColor styles.
Full code after the jump.
<?xml version="1.0"?>
<!-- http://blog.flexexamples.com/2008/01/17/setting-the-background-color-and-background-alpha-on-a-flex-popupbutton-controls-pop-up-menu/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="vertical"
verticalAlign="top"
backgroundColor="white">
<mx:Script>
<![CDATA[
import mx.controls.Menu;
import mx.events.MenuEvent;
[Bindable]
private var menu:Menu;
private function initMenu():void {
menu = new Menu();
menu.dataProvider = arr;
menu.setStyle("themeColor", "black");
}
]]>
</mx:Script>
<mx:Array id="arr">
<mx:Object label="Button" />
<mx:Object label="ButtonBar" />
<mx:Object label="ColorPicker" />
<mx:Object label="ComboBox" />
</mx:Array>
<mx:Style>
.myPop {
backgroundAlpha: 0.7;
backgroundColor: black;
borderStyle: none;
color: white;
}
</mx:Style>
<mx:ApplicationControlBar dock="true">
<mx:PopUpButton id="popUpButton"
label="Select a control..."
popUp="{menu}"
popUpStyleName="myPop"
preinitialize="initMenu();" />
</mx:ApplicationControlBar>
<mx:VBox backgroundColor="haloSilver"
width="100%"
height="100%" />
</mx:Application>
View source is enabled in the following example.

{ 2 comments… read them below or add one }
awesome ……………it helped……..saved my day……..thanks
Thanks, the common error is thinking about it as an percent value (70%), and here we can see that it is a decimal value (0.7).