Flower, as it happens, coloured yellow (4-7)
I believe the answer is:
lily-livered
'yellow' is the definition.
(I know that yellow can be written as lily-livered)
'flower as it happens coloured' is the wordplay.
'flower' becomes 'lily' (I've seen this in another clue).
'as it happens' becomes 'live' (as in live television).
'coloured' becomes 'red' (similar in meaning).
'lily'+'live'+'red'='LILY-LIVERED'
(Other definitions for lily-livered that I've seen before include "Yellow" , "chicken" , "Weak and cowardly" .)