colouring in
/ˌkʌl(ə)rɪŋ ˈɪn/(US coloring in) British, Australian, and NZ
noun
The action of filling in an outline drawing with colour using pens, crayons, etc., especially as done by a child.
Origin
1970s. From colouring + in, after to colour in. With colouring-in book compare earlier colouring book.