Petals can be of such colours (6)
I believe the answer is:
pastel
'such colours' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'petals can be' is the wordplay.
'can be' is an anagram indicator.
'petals' with letters rearranged gives 'PASTEL'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for pastel that I've seen before include "Of a colour, subtle" , "Crayon - gentle shade of colour" , "A light delicate shade of colour" , "Delicate and pale in colour" , "Chalky crayon" .)