food colouring vs colouring

food colouring and colouring both are nouns.

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

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

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

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

food colouring (noun)	colouring (noun)
a digestible substance used to give color to food	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