Long time ago when I was using Cosmos, I fell in love with the way the health bars changed colours as health went down.
When I quit using Cosmos, I copied the HealthBar.xml from Cosmos into a FrameXML directory and there it's settled since the game came out.
Now, as Cairenn will be glad to tell you, overwriting FrameXML is BAD, and it's going away, so I took notice of my existing HealthBar.xml and resolved to make it an add-on. And here it is. I'll note that the functionality is already present in Blizzard's UI (look at the .lua, it's only passing a different argument to the existing function) so if there's an option to make it look right, I'd be glad to know about it.
Color HealthBar, now available for download:
http://www.wowinterface.com/download...php?s=&id=4236
Not planning on anything fancy here, but if you notice a bug let me know.