Petals can show such shades (6)
I believe the answer is:
pastel
'such shades' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'petals can' is the wordplay.
'can' indicates an anagram (I've seen 'canned' mean this (canned can mean drunk)).
'petals' with letters rearranged gives 'PASTEL'.
'show' is the link.
Can you help me to learn more?
(Other definitions for pastel that I've seen before include "Pleats of a light colour" , "Crayon - of soft shades" , "A light delicate shade of colour" , "Delicate shade; crayon" , "Delicate and pale in colour" .)