Colour of cowardice? (6)
I believe the answer is:
yellow
'colour of cowardice?' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for yellow that I've seen before include "Chicken" , "Lemon shade" , "Fearful - colour" , "Colour of egg yolk and cowardice" , "(Of paper) age" .)