<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/08/25/setting-the-background-color-of-the-richtexteditor-text-area-in-flex/ -->
<mx:Application name="RichTextEditor_backgroundColor_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Style>
        RichTextEditor {
            textAreaStyleName: rteTextAreaStyles;
        }

        .rteTextAreaStyles {
            backgroundColor: haloSilver;
        }
    </mx:Style>

    <mx:RichTextEditor id="richTextEditor" />            

</mx:Application>