I take a lot of pictures on my iPhone, more than even my professional Nikon d200 camera. One of the many things I love about iPhone photography is the plethora of free apps available to edit and generally mess around with pictures. I've always loved those black and white pics with just an accent of color. The best and easiest to use app I've found for this is Color Effects. Other apps I've used have you, for example, define a color to keep. This results in splotchy coloring due to varying tones and shadows, and generally doesn't produce the desired affect. Color Effects let's you "paint" back the color in a photo turned black and white. You can take a picture, choose one from your photo library, or even get one from your facebook. The app allows you to zoom in and choose brush size allowing for precise coloring. It's by far the easiest and most efficient of similar free apps I've used. Below are a before and after example. This app is fun, easy to use, and free so give it a try!