skin color vs skin colour

skin color and skin colour both are nouns.

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

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

Other synonyms of skin color include complexion.

skin color (noun)	skin colour (noun)
the coloring of a person's face	the coloring of a person's face