Keep yellow tops after wearing black (4)
I believe the answer is:
inky
'black' is the definition.
('inky' can be similar in meaning to 'black')
'keep yellow tops after wearing' is the wordplay.
'tops' says to take the initial letters.
'after' is a charade indicator (letters next to each other).
'wearing' becomes 'in' (wear in (and 'in' is fashionable)**).
The first letters of 'keep yellow' is 'ky'.
'ky' put after 'in' is 'INKY'.
(Other definitions for inky that I've seen before include "Marked by leaky pen" , "Completely dark" , "Black as pen fluid?" , "Black; drunk (Aus. sl.)" , "Coloured black" .)