We have success with colour (5)
I believe the answer is:
white
'colour' is the definition.
(white is a kind of colour)
'we have success' is the wordplay.
'have' means one lot of letters goes inside another.
'success' becomes 'hit' (hit is a kind of success).
'we' enclosing 'hit' is 'WHITE'.
'with' is the link.
(Other definitions for white that I've seen before include "See 10" , "The colour of snow" , "murderer" , "Colour of milk" , "See 9" .)