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.
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 don't like the presets, there are all sorts of manual settings.
Photo editing can be subtle or pushed to the limit. Every user will find something that they like. You can make infinite changes and tapping on a new effect will wipe the old one until you hit the "apply" button. Then you can send your creation out via the usual social networks, email or save it to the camera roll.
I've seen a lot of filtering and editing tools, but I have to say iColorama has some of the most varied and powerful effects I've encountered in an app. These effects aren't for every photo, and it is easy to go overboard, but what is overboard for one person is subtle for another.