Skin pigment (7)
I believe the answer is:
melanin
'skin pigment' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for melanin that I've seen before include "Pigment that accounts for skin colour" , "tanning agent" , "Pigment causing tanning" , "Light-absorbing skin pigment" , "Pigment responsible for tanning" .)