color by number (plural color by numbers)
(usually used attributively) A simple drawing 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.
(uncountable) A technique that applies such exercises, as used until recently in the production of large-scale animations for instance.


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