<?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:Style>
        Button {
            skin: ClassReference(null);
            upSkin: ClassReference(null);
            overSkin: ClassReference("mx.skins.halo.ButtonSkin");
            downSkin: ClassReference("mx.skins.halo.ButtonSkin");
            disabledSkin: ClassReference("mx.skins.halo.ButtonSkin");
            icon: Embed("assets/Button.png");
        }
    </mx:Style>

    <mx:Button id="btn"
            label="Button" />

</mx:Application>