Damien Erambert has released iTunes 109, a simple installer package that will revert the gray iTunes 10 user interface back to the colorful one of iTunes 9.
The package will let you choose whether to change the UI of the entire application or just the side bar.
I agree the iTune 10 UI looks depressing and iTunes 9 UI looks better than iTunes 10. Thank you for the solution you brought back color to iTunes. Apple should had change the iTune 10 release name to iCancer 10.