Painter Smurf is able to paint objects blue, red, and white when he has been unlocked. To unlock the other colours you must complete the corresponding image in the Painter Smurf's mini-game at a 'Close To Perfection' rank (colors cannot be unlocked in Practice mode).

Brown
Complete an image of a Lamp Post.

Dark Blue
Complete an image of some Mushrooms.

Green
Complete an image of Smurfette.

Grey
Complete an image of a Well.

Maroon
Complete an image of a Smurf Hut.

Pink
Complete an image of Papa Smurf.

Sky Blue
Complete an image of some Flowers.

Violet
Complete an image of a Cake.

Yellow
Complete an image of a Gift Box.