Auto highlights (6)
I believe the answer is:
chrome
'auto highlights' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for chrome that I've seen before include "Hard stuff for plating - yellow pigment" , "Shiny metallic coating" , "'Silvery metal, resists tarnishing (6)'" , "Plate (for bathroom fixtures etc)" , "Decorative plating" .)