In Foliobook 2.0 onwards we removed the coloured cloth background art from the app so that its quicker to download and install. If you want/need to use the included backgrounds, please download them from here. Just right click and ‘Download link as’ to save the background to your computer, then copy into your iTunes photos sync folder and sync like a regular photo. You can then add as a background from Foliobook.
Please note, these were created for the iPad 1 so the sizing may not be appropriate for the retina screen of the iPad3, that depends on your taste, because these backgrounds are textured some people may find them fine on a retina screen.