After blue, die suffering? Poison? (7)
I believe the answer is:
cyanide
'poison?' is the definition.
(cyanide is poisonous)
'after blue die suffering?' is the wordplay.
'after' is a charade indicator (letters next to each other).
'blue' becomes 'cyan' (I have seen 'Greenish blue ' mean 'cyan' so perhaps 'blue' could also mean 'cyan').
'suffering?' is an anagram indicator.
'die' with letters rearranged gives 'ide'.
'cyan' next to 'ide' is 'CYANIDE'.
(Other definitions for cyanide that I've seen before include "Extremely poisonous salt" , "Highly toxic substance" , "Nice day (anag) - poison" , "Poisonous compound" , "killer" .)