<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/05/23/setting-the-focus-alpha-on-a-numericstepper-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.events.NumericStepperEvent;

            private function numericStepper_change(evt:NumericStepperEvent):void {
                numericStepper.setStyle("focusAlpha", evt.value);
                // reset focus
                focusManager.setFocus(btn);
                focusManager.setFocus(numericStepper);
            }
        ]]>
    </mx:Script>

    <mx:ApplicationControlBar dock="true">
        <mx:Button id="btn" label="click here to remove focus" />
    </mx:ApplicationControlBar>

    <mx:NumericStepper id="numericStepper"
            minimum="0.0"
            maximum="1.0"
            value="0.5"
            stepSize="0.1"
            textAlign="center"
            change="numericStepper_change(event);" />

</mx:Application>