Petals changed colour (6)
I believe the answer is:
pastel
'colour' is the definition.
(I know that pastel is a type of colour)
'petals changed' is the wordplay.
'changed' is an anagram indicator.
'petals' with letters rearranged gives 'PASTEL'.
(Other definitions for pastel that I've seen before include "A light delicate shade of colour" , "Staple light colour" , "pigments mixed with gum" , "Outmoded" , "Crayon - pale colour" .)