primary colour vs colouring

primary colour and colouring both are nouns.

Word	Noun	Adjective	Verb	Adverb
primary colour	Yes	No	No	No
colouring	Yes	No	No	No

As nouns, colouring is a hypernym of primary colour; that is, colouring is a word with a broader meaning than primary colour:

primary colour: any of three colors from which all others can be obtained by mixing
colouring: a visual attribute of things that results from the light they emit or transmit or reflect

Other hypernyms of primary colour include color, coloring, colour.

primary colour (noun)	colouring (noun)
any of three colors from which all others can be obtained by mixing	the act or process of changing the color of something
	a visual attribute of things that results from the light they emit or transmit or reflect
	a digestible substance used to give color to food