In iTunes 10, the icons in the sidebar have gone from colorful to drab light-grey. To some eyes, that change makes the icons harder to distinguish. If you're one of them, you might be interested in a tip from an anonymous Mac OS X Hints reader that implements an alternative colour scheme:
If you are struggling with the new low contrast icons in iTunes 10, here is a hint to change their appearance. After quitting iTunes, open Terminal and enter:
defaults write com.apple.iTunes high-contrast-mode-enable -bool TRUE
When you restart iTunes, you'll have a high contrast sidebar and list pane. To undo it, repeat the command but change the TRUE to FALSE.
By "high contrast," this tipster means, "stark black and white." Many users who have tried this tip say they like the results less than the new all-grey and so undo it. It doesn't look great in the new default Album List view (View -> As Album List or Option-Command-4). It looks better (relatively speaking) in plain List View (View -> As List or Option-Command-3).