Prisoner has lips of a deep red colour (7)
I believe the answer is:
crimson
'a deep red colour' is the definition.
(I've seen this before)
'prisoner has lips' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'has' is an insertion indicator.
'lips' becomes 'rims' ('rim' can be a synonym of 'lip').
'con' placed around 'rims' is 'CRIMSON'.
'of' acts as a link.
(Other definitions for crimson that I've seen before include "Bright red" , "Flushed" , "Looking embarrassed" , "Become red-faced" , "Microns of colour" .)