iColorama is a photo colorizing app on steroids. It has a vast array of features, from basic editing like saturation, cropping and editing, to all kinds of color and distortion effects.
The app comes in two versions, one for iPad (US$2.99) and one for iPhone ($1.99). I did most of my exploring on the iPhone version.
Although there are tutorials available, the app is straightforward. Load or take a photo, then get to work. Options scroll across the top of the screen, and when you select a process you will see more options and presets at the lower right. If you