It seems Apple plan to persist with the leather clad look of Calendar and Contacts (formerly iCal and Address Book) in ML. Personally I really don't like this and I created a patch for Lion to give an Aluminium look to them. I have now done the same for Mountain Lion for any like-minded folks. I hope its ok to post a link here, the patch is free and is tested on Mountain Lion Preview 3 and will be updated with each apple update (probably). http://macnix.blogspot.co.uk/2012/05/change-mac-os-108-mountain-lion.html Hope others find it useful.