With Mac OS X Lion, iCal and Address Book got a leather-type texture. Some people aren’t fans. You can easily get rid of it, and have it replaced with the grey/steel look of the other OS X windows.
All you have to do is download an application called Lion Tweaks. It’s available for free, but the developer does take donations. If you think the app is worth downloading, give it a shot. Maybe even support the developer by donating so that he or she can continue to make cool applications for OS X.