When I got my Nokia 808 PureView, one of the app pre-installed on it is the ColorizIt app, it allows you to turn a photo to black and whitea nd then bring out the color of any object in the photo.
I know there thousands of photo editing apps like this but this one is pre-installed on the 808 and I love it, I'm pretty addicted to it.
Its UI is pretty basic, though for a tech savvy guy like me, it did take quite a bit of practice to get used to it, it's not intuitive at first use but once you get it, it's a breeze.
The UI has a Re-Do button, a brush size button, exit and tool selection button.
You can load a pic from your gallery by clicking the "Load Photo" and you can either save the photo after editing or share it on your Facebook or Flickr.
It can take minutes to hours to finish editing a photo depending on how complicated the editing you are trying to do is.
For instance, here is an easy edit photo, I edited under 2mins...
In the image below, it took about 20mins to finish editing.
The good news is that even if you close the app, it automatically saved what ever progress you have made, so don't be scared if you think you might have lost everything after accidentally closing the app, you also can manually save a "work in progress" and continue later.
Here is a video demo of this superb app:
So far, I am unable to find the app in the Nokia Store, It comes pre-installed on US version of the Nokia 808, it could be available in the Nokia store in your region though.