Reprobate, said to go to pub, becoming bright red (8)
I believe the answer is:
cinnabar
'bright red' is the definition.
(I've seen this before)
'reprobate said to go to pub' is the wordplay.
I cannot quite see how this works, but
'pub' could be 'inn' (I've seen this before) and 'inn' is found within the answer.
This may be the basis of clue (or it may be nonsense).
'becoming' acts as a link.
Can you help me to learn more?
(Other definitions for cinnabar that I've seen before include "Red mercury sulphide" , "Brian can make vermilion pigment" , "Heavy red mineral containing mercury" , "Bright red mineral containing mercury" .)