Nutmeg's theme initially missed, showing lack of perception (6)
I believe the answer is:
myopic
'showing lack of perception' is the definition.
(myopia is short-sightedness)
'nutmeg's theme initially missed' is the wordplay.
'nutmeg's' becomes 'my' (where the crossword setter is 'Nutmeg').
'theme' becomes 'topic' (synonyms).
'initially missed' means to remove the first letter.
'topic' with its first letter removed is 'opic'.
'my'+'opic'='MYOPIC'
(Other definitions for myopic that I've seen before include "Imprudent" , "needing help from lens" , "Nearsighted" , "Lacking foresight?" , "Short-sighted" .)