A corny anagram, but it's colourful (6)

I believe the answer is:

crayon

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'it's colourful' is the definition.
I can't tell whether this definition defines the answer.

'a corny anagram' is the wordplay.
'anagram' indicates anagramming the letters.
'a'+'corny'='acorny'
'acorny' is an anagram of 'CRAYON'.

'but' is the link.

Can you help me to learn more?

(Other definitions for crayon that I've seen before include "Stick to colour" , "drawer" , "One colours with this" , "Drawing pen" , "pencil (13) [FRENCH]" .)

I've seen this clue in the Evening Standard.

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