Colourant is an ingredient of vanilla (4)
I believe the answer is:
anil
'colourant' is the definition.
I can't judge whether this definition defines the answer.
'an ingredient of vanilla' is the wordplay.
'an ingredient of' says the answer is hidden in the clue.
'ANIL' is hidden in the letters of 'vanilla'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for anil that I've seen before include "Colouring" , "Source of dye" , "A blue dye" , "Indian man" , "West Indian shrub, source of indigo" .)