I have an app with multiple panels (one is a Tree).
I'd like to have a different skin applied if the panel is the active panel. Or is it a more sensible situation to use the the same skin but apply another fill for the active titleheader
Has anyone any examples of how this can be achieived?
Sounds like you want to change the appearance on focus change. Try to overload the Panel.focusInHandler() and Panel.focusOutHandler() functions. What you want to do inside of those is change the appearance. Change the skinClass, set styles, or whatever else.
If you're using Flex 4, it sounds like skin states should solve your problem.