Cilla changed colour (5)
I believe the answer is:
lilac
'colour' is the definition.
(lilac is a shade of purple)
'cilla changed' is the wordplay.
'changed' indicates an anagram.
'cilla' with letters rearranged gives 'LILAC'.
(Other definitions for lilac that I've seen before include "Shrub with fragment purple or white flowers" , "Shrub or small tree with fragrant blossom" , "Pale purple - flowering tree" , "Light-purple" , "Tree with pink blossoms" .)