Reddish purple (7)
I believe the answer is:
'reddish purple' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for magenta that I've seen before include "Purplish-pink colour" , "Reddish purple" , "Colour named after a bloody 1859 battle in Italy" , "Light purplish-red" , "Reddish-purple colour" .)