Green, natural, timeless (5)

I believe the answer is:

naive

'green' is the definition.
(green can mean naive or innocent)

I don't understand the rest of the clue.

(Other definitions for naive that I've seen before include "Unenlightened" , "Ingenuous, easily deceived" , "Gullible, too trusting" , "Rather too simple and gullible" , "Too trusting and impractical" .)

I've seen this clue in The Guardian.

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