achromatic color vs colouring

achromatic color and colouring both are nouns.

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

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

achromatic color: a color lacking hue; white or grey or black
colouring: a visual attribute of things that results from the light they emit or transmit or reflect

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

achromatic color (noun)	colouring (noun)
a color lacking hue; white or grey or black	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