Cry, sad, having left common looking ill (6)
I believe the answer is:
yellow
'left common looking ill' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
'cry sad' is the wordplay.
'cry' becomes 'yell' (synonyms).
'sad' becomes 'ow' (I can't explain this - if you can you should give a lot more credence to this answer).
'yell'+'ow'='YELLOW'
'having' acts as a link.
Can you help me to learn more?
(Other definitions for yellow that I've seen before include "Cowardly (colloq.)" , "Snooker ball" , "egg is partly this" , "Colour of Malvolio's stockings (T. Night)" , "Cowardly - kind of fever" .)