A suggestion ... [RoboBrush]

please check this software : mediachance robobrush
If you make some color controls and etc. Users can use RoboBrush for auto painting with your wonderful application.

I'll add more color picking control in the future, but I am not sure if I like doing art with such a 'robobrush'. It's not something that amazes me. I prefer people paint with free hand. There're already so many apps that do such auto-painting thing. Our goal is not to make a 'me-too' app, but to create something that this digital art world needs badly.