Dreadful nuisance - I ignored subtle shades (7)
I believe the answer is:
nuances
'subtle shades' is the definition.
(I've seen this before)
'dreadful nuisance i ignored' is the wordplay.
'dreadful' indicates anagramming the letters.
'ignored' indicates named letters should be taken away.
'nuisance' with 'i' taken away is 'nusance'.
'nusance' is an anagram of 'NUANCES'.
(Other definitions for nuances that I've seen before include "Subtle distinctions or variations" , "suggestions" , "Suspicion of" , "subtle shades" , "'Subtle variations, in meaning perhaps (7)'" .)