Chicken or canary (6)
I believe the answer is:
yellow
I believe this is a triple definition!
'chicken' is the first definition.
(as in cowardly)
'or' is the second definition.
('or' is the heraldic name for gold or yellow)
'canary' is the third definition.
(thesaurus)
(Other definitions for yellow that I've seen before include "show sign of age" , "Colour of sunflowers and ripe lemons" , "Fearful - colour" , "Part of egg" , "'Caution' colour" .)