Muted, odd new pants acquired by fashionable people (5,4)
I believe the answer is:
toned down
'muted' is the definition.
('tone down' can be a synonym of 'mute')
'odd new pants acquired by fashionable people' is the wordplay.
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'acquired by' means one lot of letters goes inside another.
'fashionable people' becomes 'ton' ('the ton' could once mean fashionable society).
'odd'+'new'='oddnew'
'oddnew' with letters rearranged gives 'neddow'.
'neddow' going inside 'ton' is 'TONED DOWN'.
(Other definitions for toned down that I've seen before include "Less 27a [EXTREME]" , "Modest" , "Moderated; softened" , "Less harsh" .)