Tinged with sadness (11)
I believe the answer is:
bittersweet
'tinged with sadness' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for bittersweet that I've seen before include "Evoking both pleasure and pain" , "At once pleasurable and painful" , "Climber" , "arousing mixed feelings" , "Arousing pleasure tinged with pain" .)