The default style of ToolTip is really dull,so we can change this by defining our own style.
This we can do by using inline or external styles, and use the properties in this to manupulate the styles.The below example shows a simple style applyed in External.
fontFamily: Arial Black;
Now save the file as tooltip.css and include it in the flex app using the tag <style>
or define it in the <style> tag in the flex app itself. Now ur ToolTip styles are ready.
Explore with many more properties in ToolTip using the ToolTipmanager Class.