FlashBuilder 4/Flex, set transparent background for web app?

I'm embeding a flex application int开发者_如何学运维o a web page using the most recent version of swfobject.js. I've set wmode to transparent and all that but whatever I've enterd for the embeded objects default size, is then a white background within my application. I've set the application's backgroundAlpha to 0 and I know that part works because my aplication resizes after it has finished loading. The resized portion of the application is transparent but the rest still has the white background so it's obvious it has something to do with the application and not the html or javascript embedding it. How do i fix this?

Looking at the default application skin I noticed that it makes use of the backgroundColor style property to set the fill color for the backgroundRect of the applicaton. However, there's no mention of backgroundAlpha so I created a new application skin and added a single line of code which works!

Below this line:
bgRectFill.color = getStyle('backgroundColor');
Add the following:
bgRectFill.alpha = getStyle('backgroundAlpha');

In your application .mxml file set the skinClass property to:

skinClass="YourSkinsDirectory.YourApplicationSkin" 

I have mine saved as ApplicationSkin.mxml in a folder called Skins so mine looks like this: skinClass="Skins.ApplicationSkin"

Here's the full skin:

<?xml version="1.0" encoding="utf-8"?>

<!--

    ADOBE SYSTEMS INCORPORATED
    Copyright 2008 Adobe Systems Incorporated
    All Rights Reserved.

    NOTICE: Adobe permits you to use, modify, and distribute this file
    in accordance with the terms of the license agreement accompanying it.

-->

<!--- The default skin class for the Spark Application component. 

       @see spark.components.Application

      @langversion 3.0
      @playerversion Flash 10
      @playerversion AIR 1.5
      @productversion Flex 4
-->
<s:Skin xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark"
        xmlns:fb="http://ns.adobe.com/flashbuilder/2009" alpha.disabled="0.5" alpha.disabledWithControlBar="0.5">

    <fx:Metadata>
    <![CDATA[ 
        /** 
         * A strongly typed property that references the component to which this skin is applied.
         */
        [HostComponent("spark.components.Application")]
    ]]>
    </fx:Metadata> 

    <fx:Script fb:purpose="styling">
        <![CDATA[
            /**
             *  @private
             */
            override protected function updateDisplayList(unscaledWidth:Number, 
                unscaledHeight:Number) : void
            {
                bgRectFill.color = getStyle('backgroundColor');
                bgRectFill.alpha = getStyle('backgroundAlpha');
                super.updateDisplayList(unscaledWidth, unscaledHeight);
            }
        ]]>
    </fx:Script>

    <s:states>
        <s:State name="normal" />
        <s:State name="disabled" />
        <s:State name="normalWithControlBar" />
        <s:State name="disabledWithControlBar" />
    </s:states>

    <!-- fill -->
    <!--- 
        A rectangle with a solid color fill that forms the background of the application.
        The color of the fill is set to the Application's backgroundColor property.
    -->
    <s:Rect id="backgroundRect" left="0" right="0" top="0" bottom="0">
        <s:fill>
            <!--- @private -->
            <s:SolidColor id="bgRectFill" color="#FFFFFF" alpha="1"/>
        </s:fill>
    </s:Rect>

    <s:Group left="0" right="0" top="0" bottom="0">
        <s:layout>
            <s:VerticalLayout gap="0" horizontalAlign="justify" />
        </s:layout>

        <!--- 
            @private
            Application Control Bar
        -->
        <s:Group id="topGroup" minWidth="0" minHeight="0"
                    includeIn="normalWithControlBar, disabledWithControlBar" >

            <!-- layer 0: control bar highlight -->
            <s:Rect left="0" right="0" top="0" bottom="1" >
               <s:stroke>
                    <s:LinearGradientStroke rotation="90" weight="1">
                        <s:GradientEntry color="0xFFFFFF" />
                        <s:GradientEntry color="0xD8D8D8" />
                    </s:LinearGradientStroke>
               </s:stroke>
            </s:Rect>

            <!-- layer 1: control bar fill -->
            <s:Rect left="1" right="1" top="1" bottom="2" >
               <s:fill>
                    <s:LinearGradient rotation="90">
                        <s:GradientEntry color="0xEDEDED" />
                        <s:GradientEntry color="0xCDCDCD" />
                    </s:LinearGradient>
               </s:fill>
            </s:Rect>

            <!-- layer 2: control bar divider line -->
            <s:Rect left="0" right="0" bottom="0" height="1" alpha="0.55">
                <s:fill>
                    <s:SolidColor color="0x000000" />
                </s:fill>
            </s:Rect>

            <!-- layer 3: control bar -->
            <!--- @copy spark.components.Application#controlBarGroup -->
            <s:Group id="controlBarGroup" left="0" right="0" top="1" bottom="1" minWidth="0" minHeight="0">
                <s:layout>
                    <s:HorizontalLayout paddingLeft="10" paddingRight="10" paddingTop="7" paddingBottom="7" gap="10" />
                </s:layout>
            </s:Group>
        </s:Group>

        <!--- @copy spark.components.SkinnableContainer#contentGroup -->
        <s:Group id="contentGroup" width="100%" height="100%" minWidth="0" minHeight="0" />

    </s:Group>

</s:Skin>