subtlety

(noun) a subtle difference in meaning or opinion or attitude. Synonyms: nuance, nicety, shade, refinement. Examples: "Without understanding the finer nuances you can't enjoy the humor." "Don't argue about shades of meaning."

(noun) the quality of being difficult to detect or analyze. Synonyms: niceness. Example: "You had to admire the subtlety of the distinctions he drew."