Restrained, subdued (3-3)
I believe the answer is:
low-key
This clue is a double definition.
'restrained' is the first definition.
(similar in meaning)
'subdued' is the second definition.
(synonyms)
(Other definitions for low-key that I've seen before include "Modest, restrained" , "Lacking intensity" , "Restrained, not intense or emotional" , "Unemphasised" , "Understated" .)