Very dark in Kentucky (4)
I believe the answer is:
inky
'very 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 "Like writing fluid" , "Marked by leaky pen" , "Like the printing trade" , "Coloured black" , "Jet" .)