Hi,
What you're looking for is called "conditional formatting". Here is a Youtube link to how to do it in Outlook 2010:
https://www.youtube.com/watch?v=zuudD32RxU4 In Outlook 2007 it is a similar process but you start with the "View" menu item.
Mike Sperry
http://www.SperrySoftware.com
Find 37 Outlook add-ins that can make a difference!