Colour as used by Spencer is eye-catching (6)
I believe the answer is:
cerise
'colour' is the definition.
(I know that cerise is a type of red)
'used by spencer is eye-catching' is the wordplay.
'used by' says the answer is hidden in the clue.
'CERISE' is hidden in the letters of 'spencer is eye catching'.
'as' acts as a link.
(Other definitions for cerise that I've seen before include "Shade of red" , "Reddish-pink colour" , "Bright cherry-red colour" , "Deep red colour" , "Cherry red colour" .)