primary color vs primary colour

primary color and primary colour both are nouns.

Word	Noun	Adjective	Verb	Adverb
primary color	Yes	No	No	No
primary colour	Yes	No	No	No

As nouns, primary color and primary colour are synonyms defined as:

primary color and primary colour: any of three colors from which all others can be obtained by mixing

primary color (noun)	primary colour (noun)
any of three colors from which all others can be obtained by mixing	any of three colors from which all others can be obtained by mixing