Instead of having a tranparent background like this:
...my GNOME Activities Overview is having a solid black background. How can I get the transparency?
I figured it out. It seems to be a bug of the proprietary
Well it may be something that you can enable via Ubuntu Tweak, I managed to get my top bar to be transparent on Ubuntu Tweak but I'm on the Unity graphical interface so UTweak may not be compatible with GNOME for all I know.
But anyway, heres the link to the Ubuntu Tweak site: http://ubuntu-tweak.com/
hope this works, if it doesn't then sorry
Happy Ubuntuing =D