Change colour but fade away utterly (3)
I believe the answer is:
dye
'change colour' is the definition.
(I've seen this before)
'fade away utterly' is the wordplay.
'fade away' becomes 'die' (I've seen this in another clue).
'utterly' shows a homophone (sound like) (as uttered).
'die' is a homophone of 'DYE'.
'but' acts as a link.
(Other definitions for dye that I've seen before include "Colour or stain something" , "Colouring matter" , "Tint" , "Colorant" , "Soluble substance for staining or colouring" .)