Reddish-brown hair colour (6)
I believe the answer is:
auburn
'reddish-brown hair colour' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for auburn that I've seen before include "Red-brown hair colouring" , "Goldsmith: 'Sweet . . . . . . loveliest village of the plain'" , "Golden" , "Reddish-brown hair colour" , "Reddish-brown, hair say" .)