Here we got to use a property to apply style to our Date Field control.
dateChooserStyleName -> property to use
use it as:
<mx:DateField id=”dateField”
dateChooserStyleName=”subDateChooser” />
Now define ur style like below with properties of your like.
<mx:Style>
.subDateChooser {
backgroundColor: black;
color: white;
fontweight:bold
}
</mx:Style>
Now the Date Field control has the style we have defined.
This gives the snapshot,enjoy the code.
Posted by kumargandhi 
