<?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" viewSourceURL="srcview/index.html">

    <mx:Button id="btn"
            label="Button"
            skin="{null}"
            upSkin="{null}"
            overSkin="mx.skins.halo.ButtonSkin"
            downSkin="mx.skins.halo.ButtonSkin"
            disabledSkin="mx.skins.halo.ButtonSkin"
            icon="@Embed('assets/Button.png')" />

</mx:Application>