I found a very nice photo editing app! It has more features than you can possibly expect from one single android app in the current time.
Photo Editor by Aviary is equipped with enhancement features that really do the job. They practically change your picture for better. They reveal photo details and improve the color and contrast.
Another really nice feature of Photo Editor by Aviary is splash. With splash you can choose which parts of the pic should be in color and and which parts should be in B/W.