Lobster getting on a coloured pencil (6)

I believe the answer is:

crayon

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'a coloured pencil' is the definition.
(I've seen this before)

'lobster getting on' is the wordplay.
'lobster getting' becomes 'cray' (I am not sure about this - if you are sure you should believe this answer much more).
'cray'+'on'='CRAYON'

Can you help me to learn more?

(Other definitions for crayon that I've seen before include "Coloured wax pencil" , "pencil (13) [FRENCH]" , "Colouring pencil" , "Drawing-stick" , "Drawing pen" .)

I've seen this clue in the Sydney Morning Herald.

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