Dark in Kentucky (4)
I believe the answer is:
inky
'dark' is the definition.
(I've seen this before)
'in kentucky' is the wordplay.
'kentucky' becomes 'ky'.
'in'+'ky'='INKY'
(Other definitions for inky that I've seen before include "Jet" , "Dark; stained" , "Black as pen fluid?" , "Leaked on by pen" , "Pitch-black" .)