colouring vs food colouring

colouring and food colouring both are nouns.

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

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

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

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

colouring (noun)	food colouring (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