In WebSphere Service Repository and Registry V8, the Business Space UI changed how custom themes are added. Before you would put a file somewhere on the disk and set a variable in WebSphere Application Server to where the file is. You can change the login page, banners and add new colours and style graphics.
Now you use WebDAV to upload files to Business Space, then update configuration in WebSphere Application Server to point to the new theme.
The Business Space infocenter goes into a lot more detail: