Pair back in plant become dull (5,4)

I believe the answer is:

cloud over

'become dull' is the definition.
(the weather becoming dull)

'pair back in plant' is the wordplay.
'pair' becomes 'duo' (two people).
'back' says the letters should be written in reverse.
'in' means one lot of letters goes inside another.
'plant' becomes 'clover' (clover is a kind of plant).
'duo' reversed gives 'oud'.
'oud' placed into 'clover' is 'CLOUD OVER'.

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.