color constancy vs colour constancy

color constancy and colour constancy both are nouns.

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

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

color constancy and colour constancy: the tendency for a color to look the same under widely different viewing conditions

color constancy (noun)	colour constancy (noun)
the tendency for a color to look the same under widely different viewing conditions	the tendency for a color to look the same under widely different viewing conditions