I installed Vista RTM and played around with Sidebar. My graphics card was
poor, so I didn't get the Aero effect anywhere. Sidebar had a solid, dark
grey background.

Now I've installed a better graphics card and Aero is on everywhere.
However, Sidebar is just getting darker and darker. It looks like it's
compositing the newer look over and over on the non-Aero background.

How can I reset it and get the Aero look?