Dreadful nuisance - I lost subtle shades (7)
I believe the answer is:
nuances
'subtle shades' is the definition.
(I've seen this before)
'dreadful nuisance i lost' is the wordplay.
'dreadful' is an anagram indicator.
'lost' indicates named letters should be taken away.
'nuisance' with 'i' taken out is 'nusance'.
'nusance' anagrammed gives 'NUANCES'.
(Other definitions for nuances that I've seen before include "subtle shades" , "Subtleties" , "Fine shades (of meaning)" , "Subtle differences" , "Subtle distinctions or variations" .)