food colouring vs food color

food colouring and food color both are nouns.

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

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

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

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

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