food colouring vs food colour

food colouring and food colour both are nouns.

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

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

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

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

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