primary color vs colouring

primary color and colouring both are nouns.

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

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

primary color: 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 color include color, coloring, colour.

primary color (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