What's inside the white flower? (4)
I believe the answer is:
iris
This clue is a double definition.
'what's inside the white' is the first definition.
(irises are in the whites of the eyes)
'flower?' is the second definition.
(thesaurus)
(Other definitions for iris that I've seen before include "Flag or flower in the eye" , "pupil's governor" , "bit of a looker" , "Eye part or pretty flower" , "plant with showy flowers" .)