<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/08/20/changing-the-default-skins-on-a-button-control-in-flex/ -->
<mx:Application name="Button_upSkin_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.skins.halo.ButtonSkin;

            [Embed("assets/Button.png")]
            private const buttonIcon:Class;

            private function init():void {
                btn.setStyle("skin", null);
                btn.setStyle("upSkin", null);
                btn.setStyle("overSkin", ButtonSkin);
                btn.setStyle("downSkin", ButtonSkin);
                btn.setStyle("disabledSkin", ButtonSkin);
                btn.setStyle("icon", buttonIcon);
            }
        ]]>
    </mx:Script>

    <mx:Button id="btn"
            label="Button"
            initialize="init();" />

</mx:Application>