Fop in red and yellow (5)
I believe the answer is:
dandy
'fop' is the definition.
(I know that fop can be written as dandy)
'in red and yellow' is the wordplay.
'in' says the answer is hidden in the clue.
'DANDY' is hidden within 'red and yellow'.
(Other definitions for dandy that I've seen before include "Man about town" , "Beau" , "Foppish man" , "Fashionable fellow" , "Showy dresser" .)