Turn pale. Guilty perhaps? (4)
I believe the answer is:
plea
'guilty perhaps?' is the definition.
(I've seen this before)
'turn pale' is the wordplay.
'turn' is an anagram indicator.
'pale' with letters rearranged gives 'PLEA'.
(Other definitions for plea that I've seen before include "Defendant's answer to a charge or claim" , "Earnest appeal" , "Excuse - pretext" , "Humble request for help" , "Heartfelt request" .)