British spelling vs off-colour

British spelling is a noun but off-colour is not a noun.

Word	Noun	Adjective	Verb	Adverb
British spelling	Yes	No	No	No
off-colour	No	Yes	No	No

British spelling (noun)	off-colour (noun)
English orthography used in the UK, Ireland and most of the Commonwealth (characterized by 'analyse', 'centre' and 'useable')

British spelling (adjective)	off-colour (adjective)
	in violation of good taste even verging on the indecent