Skin pigment; lineman (anag.) (7)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
melanin
(Other definitions for melanin that I've seen before include "Pigment that accounts for skin colour" , "tanning agent" , "Brown skin pigment" , "Tanning pigment in skin" , "Light-absorbing skin pigment" .)