The besetting sin of the Greens? (4)

I believe the answer is:

envy

I'm a little stuck... Click here to teach me more about this clue!

'sin of the greens?' is the definition.
'envy' can be an answer for 'sin' (envy is a kind of sin). I am not certain of the 'of the greens?' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for envy that I've seen before include "Covet; be jealous of" , "Desire of another's property etc" , "One of seven deadly sins" , "The green-eyed emotion" , "Jealous longing" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app