Colorize was one of the first apps to do colorizing (you know where it turns it black and white but keeps some things in color) and was initially demoed by Microsoft. Well now it’s free:
Get creative. Make your pictures unique by colorizing them! Convert an image to black and white and then bring back a pop of color wherever you choose by brushing or flooding the color back on with your fingertip. You can zoom in and rotate the image and change only the smallest details or you can enlarge the brush size and swipe across it sloppily. Your creation is sure to be unique and it’s super easy to do. You can grab an image from the Picture hub by simply viewing it and selecting the colorize option from the extras menu or you can start in the app and take a new picture or find an existing one. You can start your work and leave it half done by saving it as a project and when you get back to it, you just continue. When finished, you simply save your new creation as an image and you’ll find it back in your Picture hub. Don’t forget to email or post it for others to enjoy.
* Mango support with fast switching
* Performance optimization makes editing even smoother
* Flood Fill (a.k.a bucket tool) auto-fills areas to make colorizing easier
* Adjustable Color Tolerance for Flood feature from high, which floods large less similar areas to low, which floods smaller more similar areas
* Tap to center and reset image to original size
* Status display shows tool and edit mode being used
* Take a picture from within the app
* Pinch to Zoom
* Pan and rotate
* Unlimited Undo
* Save projects to maintain work in progress
* Change brush size from pencil tip to thumb
* Switch back and forth between color and black & white brush to make corrections
I actually paid for this a long time ago and it’s a great app. You can get all of the details here.