New Compiz transparency

Caveat lector: I wrote this post in high school; it’s likely outdated and poorly written.

This may not be new but, after upgrading compiz from git today, I noticed that certain windows (gnome-system-monitor and the AWN manager) were semi-transparent. See the screenshot:

Edit: As far as I can tell, the Murrine engine, not compiz, is not causing the transparency.