Some practical notes times time. For my own EBS 11.5.10 installation I wanted to change the background in applications. To do this, modify the $OA_HTML/bin/appsweb.cfg
Look for 'background' and give the complete path to the gif you want to use. The gif must be placed in the $JAVA_TOP/oracle/apps/media directory.
When you bounce the webserver, youw own background should be visible.
You can also change or remove the default Oracle splash screen. In the same appsweb.cfg, look for splashscreen and comment it out or change the gif, be sure to place the new gif in the same directory.