To add colours to a black-and-white drawing, using coloured drawing equipment.(verb)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "colour in" in a sentence
"MANY people looked, a few followed, when Edith Carr slowly came down the main street of Mackinac, pausing here and there to note the glow of colour in one small booth after another, overflowing with gay curios."
"With the latter, shame, or it may be in part fear, is expressed, according to Mr. Scott, much more plainly by the head being averted or bent down, with the eyes wavering or turned askant, than by any change of colour in the skin."
"Luckily, J.B. was all for it, saying it was right and useful that Douglass should meet "our strategian", as he called me, and when Joe, inevitably, asked to come along, he agreed right off; it would be good for Douglass to see such a fine upstanding man of colour in the forefront of the cause, he said."