Confession of follower heard to get slap (3,6)
I believe the answer is:
eye shadow
'slap' is the definition.
(type of make-up - slap can mean make-up)
I can't explain the rest of the clue.
(Other definitions for eye shadow that I've seen before include "Mascara" , "This could improve your appearance" , "Coloured cosmetic" , "Facial cosmetic" , "Part of cosmetic treatment" .)