The pinch to zoom function makes it easy to zone in on tiny areas without a massive reduction in resolution, and the colouring itself is as simple as one tap to fill, another to erase. Once you've finished colouring, there are a plethora of different effects (both still and animated) you can add on to make your picture stand out. Check out the slideshow of some of these effects below.
Here is a couple of pictures I completed, they're both finished with the 'Shadow' effect as I liked that one best :)
Currently this app is only available on iTunes.