Transparency In Gnome/Metacity

Go to Gconfig editor and open apps, metacity, general and check compositing_manager.
Install transet: sudo apt-get install transset.

Using Transset for transparent windows in Gnome:

This is just an extra little command. If you want to set certain windows as transparent, then run the command "transset" in the console. Your mouse will turn into a crosshair; simply click on the window you want to set as transparent. The transparency value can be anywhere from 0 (completely transparent) to 1 (opaque.) It defaults to .75, and back to 1 if the window is already transparent.

For example, if you want to make a window half-transparent: transset 0.5.

Now make two launchers in the panel: one with command transset 0.5, the other one with transset 1.0 and you will be able the transparency mode easily.
and call them transSet and TransUndo. And you