I received an iPad from the family for Christmas and just had to have a go at finger painting.
I downloaded an app called Procreate as I had seen this before in the (in)famous, viral, Morgan Freeman finger-painting video, then messed around to see what I could do with it.
At less than $10 Australian, it's an astonishingly capable program that would give Photoshop a run for its (considerable and never-ending) money if it was ever available on the desktop.
I've uploaded a video of my first fumblings in Procreate. Don't judge the program by my efforts, though.