Malys-ex icon set is designed by Malysss from deviantart, He also made Uniblue and Uniblack icon sets. These icons are well designed, colorful and squared shaped icons, This icons set can fit with any kind of light or dark theme. Also checkout icons collection.
You can use Unity Tweak ToolGnome-tweak-tool or Ubuntu-Tweak to change icons.
malys icons

malys icons

malys icons

To install Malys-ex icons in Ubuntu 15.04/14.10/14.04/12.04/Linux Mint 17.1/17/13 open Terminal (Press Ctrl+Alt+T) and copy the following commands in the Terminal:

To install Malys-ex icons in any Ubuntu/Mint open Terminal (Press Ctrl+Alt+T) and copy the following commands in the Terminal:
That's it
Source: Malys-ex
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