Some pure deep colour (3)
I believe the answer is:
red
'colour' is the definition.
(red is a kind of colour)
'some pure deep' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'RED' is hidden within 'pure deep'.
(Other definitions for red that I've seen before include "could be a Marxist" , "Florid" , "Glowing" , "Primary colour" , "A colourful communist" .)