off-color vs off-colour

off-color and off-colour both are adjectives.

Word	Noun	Adjective	Verb	Adverb
off-color	No	Yes	No	No
off-colour	No	Yes	No	No

As adjectives, off-color and off-colour are synonyms defined as:

off-color and off-colour: in violation of good taste even verging on the indecent

Other synonyms of off-color include indelicate.

off-color (adjective)	off-colour (adjective)
humorously vulgar	in violation of good taste even verging on the indecent
in violation of good taste even verging on the indecent