Cultured and splendid in crimson (7)
I believe the answer is:
refined
'cultured' is the definition.
('refined' can be a synonym of 'cultured')
'splendid in crimson' is the wordplay.
'splendid' becomes 'fine' (I've seen this before).
'in' is an insertion indicator.
'crimson' becomes 'red' ('red' can be a synonym of 'crimson').
'fine' inserted into 'red' is 'REFINED'.
'and' is the link.
(Other definitions for refined that I've seen before include "Polished" , "Tasteful; genteel" , "Free from vulgarity" , "Just like the cultured" , "Not coarse" .)