colouring vs food colour

colouring and food colour both are nouns.

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

As nouns, colouring and food colour are synonyms defined as:

colouring and food colour: a digestible substance used to give color to food

Other synonyms of colouring include coloring, food color, food coloring, food colouring.

colouring (noun)	food colour (noun)
the act or process of changing the color of something	a digestible substance used to give color to food
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