Meaning of “colouring” - Learner’s Dictionary

colouring

noun [ U ] UK (US coloring) uk us /ˈkʌlərɪŋ/
COLOUR

the colour of something, especially an animal or person's skin, hair, and eyes:

The boys have their father's colouring.
SUBSTANCE

a substance that is used to colour something:

food/artificial colouring

(Definition of “colouring” from the Cambridge Learner’s Dictionary © Cambridge University Press)