Olive tree's beginning to develop flower (6)
I believe the answer is:
Here is my best explanation:
'flower' is the definition.
'olive tree's beginning to develop' is the wordplay.
'beginning to' suggests taking the first letters.
'develop' indicates an anagram.
The first letter of 'tree' is 't'.
'olivet' anagrammed gives 'VIOLET'.
(Other definitions for violet that I've seen before include "Bluish-purple colour as of pretty flower", "Flower; colour", "Colour; flower, source of fragrance", "Purple", "Bluish purple", "Spectrum colour", "plant", "Flower-girl", "William's girl" and "Rainbow colour; flower".)