Color Splurge - Color/Recolor/Gray/Splash Color/Colorize on images and Facebook photos and send real post cards (Free) by Vijay Doddavala is an app that allows you to convert your images to grayscale and then paint colors back on.
There are many iterations of this concept in the App Store, like Color Blast and Color Splash. While the idea behind the app isn’t novel, it is available for free, which makes it worth checking out.
You can import photos from a range of sources, including your photo library, Facebook, the pasteboard, and directly from the camera. You can zoom in using pinching gestures, and paint using a variable size paintbrush.
It’s never simple to use these apps to color photos, but this one works as well as the others. It does not, however, work in landscape mode, which means there’s less space to utilize.
With the Colorize feature, you can add colors that were not naturally in the photo, giving the entire picture a colored tint. You can use RGB sliders to choose a color or enter hex numbers. An undo button lets you fix mistakes quickly, and the revert button will return the picture to its original gray color.
Your finished photos can be uploaded in full resolution to Facebook, Twitpic, email, or the Photos app. You can also send your photos to the Sincerely app to turn them into post cards that can be printed and shipped anywhere in the world.
Of course, there is a price to pay, even for a free app. There is an ad bar at the top which is distracting and can make the app difficult to use, and when you first open the app there are popups urging you to download other games. It would be best to pay $0.99 for one of the apps that is ad free, but if don't want to spend a dollar, this is a good alternative.