Crystal Icons

From, Everaldo Coelho's website

Crystal Icons is a theme created by Everaldo Coelho for KDE, the main graphic interface for the operating system Linux, currently used on thousands of softwares and websites around the world.

Crystal theme © Everaldo Coelho - another website: Yellow Icon

Nuvola Icons

From Wikipedia, the free encyclopedia

Nuvola (from Italian "cloud", Nuvola as evolution of the SKY icon theme) is a free software / open-source software icon set drawn by David Vignoni. Originally created for desktop environments like KDE and GNOME, it was repackaged for Windows and Macintosh. The final version, 1.0, contains almost 600 icons. The default set is in the PNG graphics format; an SVG version is also available.

The application icons, in particular, colourfully represent a wide variety of commonplace and easily-recognised objects. Most icons are blue, but other colours are present as well.

It's released under terms of GNU LGPL 2.1.

Nuvola theme © David Vignoni