Mylo-Xylo icons are round colorful icons designed for Gnome desktop and based on
All-black icon set. It is under development and should not expect it as complete icon set but creator mentioned that version 1.0 will be complete set. You can also contribute to this project by going to source link and contact to creator or report any bug/missing icon to creator. You can use
Unity Tweak Tool,
Gnome-tweak-tool or
Ubuntu-Tweak to change icons.
