Use tag
<?xml version="1.0"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">
<mx:TextArea height="100" width="250">
<mx:htmlText>
<font size='20'>font size</font>,
<br><font color="#0000FF">color</font>,
<br><font face="CourierNew, Courier,Typewriter">face</font>, or
<br><font size="18" color="#FF00FF"face="Times,Times New Roman, _serif"></font>
</mx:htmlText>
</mx:TextArea>
</mx:Application>
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