green fingers vs speciality

green fingers and speciality both are nouns.

Word	Noun	Adjective	Verb	Adverb
green fingers	Yes	No	No	No
speciality	Yes	No	No	No

As nouns, speciality is a hypernym of green fingers; that is, speciality is a word with a broader meaning than green fingers:

Other hypernyms of green fingers include forte, long suit, metier, specialty, strength, strong point, strong suit.

green fingers (noun)	speciality (noun)
a special ability to make plants grow	the special line of work you have adopted as your career
	a distinguishing trait
	an asset of special worth or utility