food coloring vs food colouring

food coloring and food colouring both are nouns.

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

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

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

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

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