A free app for Android, by Yodr Studio.
The Coloring by the Numbers Coloring Book is a free drawing game where you have to fill in the color by the number of the palette. There are lots of different coloring pages to choose from and you can use both your phone and tablet to play.
The idea behind the game is simple: you have to select a palette with the matching number and then paint the page with one click. It is very easy to play and you can do lots of different things with it.