Black Knight seen in Disney regularly (4)
I believe the answer is:
inky
'black' is the definition.
('inky' can be similar in meaning to 'black')
'knight seen in disney regularly' is the wordplay.
'knight' becomes 'k'.
'seen in' means one lot of letters goes inside another.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'disney' are 'iny'.
'k' placed within 'iny' is 'INKY'.
(Other definitions for inky that I've seen before include "Black; drunk (Aus. sl.)" , "Like writing fluid" , "Like the printing trade" , "Pitch-black" , "Completely dark" .)