color by number

Noun

 * 1)  A simple coloring exercise, intended especially for children, consisting of a line drawing that divides the artwork into distinct spaces, the intended color of each indicated by a number and referenced from a key.
 * 2)  A technique that applies such exercises, as formerly used in the production of large-scale animations for instance.

Verb

 * 1) To complete such an exercise; to carry out such a technique by filling in each space with the appropriate color.