This icon theme for Gnome provides monochromatic icons for panels, toolbars and buttons and colourful squared icons for devices, applications, folder, files and Gnome menu items.

Faenza icon theme is available to install for Ubuntu Karmic and higher via a PPA, open a terminal and run:

sudo add-apt-repository ppa:tiheum/equinox
sudo apt-get update
sudo apt-get install faenza-icon-theme

You can also install the folowing packages:

* faenza-icons-mono to replace 22×22 squared icons for Deluge, Exaile, Fusion Icon, iBus and Kupfer by their monochromatic counterpart.
* faenza-extras or faenza-dark-extras to override some icons displayed in system tray by Faenza monochromatic ones. This affects Liferea, LastFM and RadioTray. Just install the package to match the theme you are using.

After installation, right-click on desktop and select “Change Desktop Background”. In “Theme” choose current theme and click “Customize…” button.

Now choose one among Faenza icons under “Icons” tab.

For more, see Faenza Icon on gnome-look.org