Painted on Nintendo 3DS with Colors! 3D app.
Two skulls have 3D effects. **All pictures all avaiable here: http://colorslive.com/author.php?id=41355 **You can download them or watch the playback. mpo files are 3D files, download them and use a 3D viewing program or put them to your 3DS. If you don't know how, use Google for help.
All of those skulls were done in 2013.
They were uploaded on Colors! Gallery and shared on Tumblr.
Let me add the artist's description.
Starting from top left:
1) Colorful Skull (because of the exaggerated colors). It has 3D effects.
2) Despite of color contrast and kind of artificial look, the pic doesn't have a tittle.
3) Strawberry Cream Skull.
4) No tittle, just a skull. It has 3D effects.
5) Dull Cyan Skull.
6) Sweet Orange Skull.
Thanks for looking.