Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Color View Finder - Real time color palette from your iphone camera
Pixilart - A drawing app for delightfully retro pixel art
A Color Story - The photo app to colourize your life
Pixel Art Studio - A purpose-built drawing tool for pixel artists
Trigraphy - Photo editing app that allows you to make mosaic/abstract looking art.