Mum clothes a nice man in purple (7)
I believe the answer is:
magenta
'purple' is the definition.
(thesaurus)
'mum clothes a nice man' is the wordplay.
'mum' becomes 'ma' ('ma' can be a synonym of 'mum').
'clothes' is an insertion indicator.
'nice man' becomes 'gent'.
'a'+'gent'='agent'
'ma' going around 'agent' is 'MAGENTA'.
'in' is the link.
(Other definitions for magenta that I've seen before include "Purplish-pink colour" , "this might be an ink" , "Colour named after a bloody 1859 battle in Italy" , "Colourful" , "Bright purplish red or magnate" .)