off-colour vs off-color

off-colour and off-color both are adjectives.

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

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

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

Other synonyms of off-colour include indelicate.

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