Here is the full list of all 13 Pixel Art Coloring Book achievements.
Color your first picture.
Open the game
Color the entire Animals category.
Color the entire Architecture category.
Color the entire Food category.
Color 10 easy pictures.
Color 10 medium pictures.
Color 10 hard pictures.
Use Magic wand 5 times.
Use Bomb 5 times.
Use Color splash 5 times.
Use Tornado 1 time.
Color 3 pictures without using boosters.