Mum clothes spy in purple (7)
I believe the answer is:
magenta
'purple' is the definition.
(I have seen 'Reddish purple' mean 'magenta' so perhaps 'purple' could also mean 'magenta')
'mum clothes spy' is the wordplay.
'mum' becomes 'ma' (both can mean mother).
'clothes' is an insertion indicator (some letters clothe or cover others).
'spy' becomes 'agent' (secret agent).
'ma' going around 'agent' is 'MAGENTA'.
'in' acts as a link.
(Other definitions for magenta that I've seen before include "Light purplish-red" , "Shade of purple" , "fuchsia" , "Colour named after a bloody 1859 battle in Italy" , "Reddish-purple colour" .)