Image Blender is a hugely popular app for creative mobile photography editing, it allows the user to combine images with masks and various blend approaches. Image Blender has just been updated with Color Filters. Image Blender will also save images taken in app to your camera roll.
This is a free update, if you have already purchased Image Blender, if not, you can download it here. It retails for $2.99/£1.99/download/update