<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/12/18/changing-the-background-color-of-the-nested-calendar-in-a-flex-datefield-control/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="top"
        backgroundColor="white">

    <mx:Style>
        .subDateChooser {
            backgroundColor: black;
            color: white;
        }
    </mx:Style>

    <mx:DateField id="dateField"
            dateChooserStyleName="subDateChooser" />

</mx:Application>