There are some users that really don’t like Apple’s use of the linen pattern background in their recent operating systems. During my daily blog reading I came across an article on Cult of Mac that shows how to customize it, at least in Notification Center.
You’ll need to go to the following folder: System/Library/CoreServices and find the Notification Center app. Right click on the application and select Show Package Contents from the menu. This will enable you to see the ‘guts’ of Notification Center. Let me warn you now that altering any of the contents of this application may cause the app to stop functioning. Proceed at your own risk!
Look for a folder called Resources, and in there, you will fins a file called linen.tiff. This is the picture file the OS uses for the background. Copy this to another location so that you have a backup and can restore the file if you want it back. To change it, you just choose another image, rename it to linen.tiff and replace the original file in the Resources folder.
To activate the image you can either restart your computer or go to Activity Monitor and quit Notification Center. The next time you open the Notification Center panel, the image should be there.
You can read the original article here.