As each lemon develops it can change colour (9)
I believe the answer is:
chameleon
'change colour' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'as each lemon develops it' is the wordplay.
'each lemon' anagrams to 'CHAMELEON'.
Though, I'm not sure how this is indicated.
'can' is the link.
Can you help me to learn more?
(Other definitions for chameleon that I've seen before include "Variable-colour reptile" , "Lizard able to change its skin colour" , "Lizard whose skin changes colour" , "fickle person" , "Person who keeps changing" .)