The Faenza 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. Four themes are included to fit with light or dark themes/panels.
To add the PPA and install the Faenza icons open a terminal window (press Ctrl+Alt+T) and copy+paste the following lines:
sudo add-apt-repository ppa:tiheum/equinox
sudo apt-get update
sudo apt-get install faenza-icon-theme
When installed you can close the terminal window and to change the icons press the SuperKey and type: advanced settings. Then click on Theme and change the Icon theme to Faenza.
If you don’t have the gnome tweak tool (advanced settings) installed, open a terminal window and copy+paste the following line:
sudo apt-get install gnome-tweak-tool