So, my iPhone app has finally been released. My work had me develop this for them over Christmas, then it kinda fell between the cracks for a bit. But, it's out now and in the wild.
The app lets you take a picture (or select a picture from your photo album), and converts it into a "coloring book," where you can select a color then touch a segment to fill it in. You can turn on and off the segment lines, and adjust how much the underlying image shows through.
If you have an iPhone, search for "ColorIt!" in the app store.