Ruby-colored (3)
I believe the answer is:
red
This clue is a double definition.
'ruby' is the first definition.
(synonyms)
'colored' is the second definition.
(similar in meaning)
(Other definitions for red that I've seen before include "could be a Marxist" , "Bordeaux claret, for instance" , "The colour of the former Russian army" , "Merchant flag" , "- Cross; - admiral" .)