A very nice extension that adds a useful focus effect on Gnome Shell was updated today reaching version 1.0!
The extension simply adds a transparency to the unfocused windows, allowing the better optical focus on the selected/clicked window. This works especially good when using using simplistic wallpapers.
A nice side effect is that every newly opened window gets a smooth transparent to solid effect for a very short period when opening. The only thing I could ask for is the ability to easier change the settings through the extension preferences.
To install this extension you can either download it, unzip the downloaded file and then put the folder into usr/share/gnome-shell/extension, or download the zip and open the Advanced Settings, go to the extensions category and open the zip by pressing the “Install Extension” button.