Several iTunes 10 users were less than thrilled with the new all-grey UI theme. I've gotten used to it, but I agree it was a bit prettier with the color icons in the sidebar. Here's how you can replace the grey entirely with an eye-popping, high-contrast black and white.
First, quit iTunes. Then open up Terminal and enter the following:
Re-launch and pow! You'll be presented with the UI depicted above. It's definitely legible, and Macworld suggests that it looks best in List View. They also explain how to switch back.defaults write com.apple.iTunes high-contrast-mode-enable -bool TRUE
We don't know if the stark theme is better, but it is different.