GNOME Bugzilla – Bug 613533
Transparency should view content directly below.
Last modified: 2010-03-21 22:11:00 UTC
If you right click a panel click properties then background and set it to transparent. It should be transparent to the window below not straight to the desktop. See a screen capture attached.
Sorry I found the bug I was looking for. *** This bug has been marked as a duplicate of bug 336122 ***