Plates changing colour (6)
I believe the answer is:
pastel
'colour' is the definition.
(pastel is a kind of colour)
'plates changing' is the wordplay.
'changing' indicates anagramming the letters.
'plates' anagrammed gives 'PASTEL'.
(Other definitions for pastel that I've seen before include "Outmoded" , "Soft shade; crayon" , "Chalky crayon" , "A light delicate shade of colour" , "Pleats of a light colour" .)