<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/09/01/customizing-a-flex-textinput-controls-error-color/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:ApplicationControlBar dock="true">
        <mx:Label text="errorColor:" />
        <mx:ColorPicker id="colorPicker" />
    </mx:ApplicationControlBar>

    <mx:Form>
        <mx:FormItem label="text:" required="true">
            <mx:TextInput id="textInput"
                    errorColor="{colorPicker.selectedColor}"
                    errorString="Custom error color" />
        </mx:FormItem>
        <mx:FormItem>
            <mx:Button />
        </mx:FormItem>
    </mx:Form>

</mx:Application>