One encapsulated by colossus in Venetian artist (6)
I believe the answer is:
titian
'venetian artist' is the definition.
(painter and member of the Venetian school)
'one encapsulated by colossus' is the wordplay.
'one' becomes 'i' (Roman numeral).
'encapsulated by' means one lot of letters goes inside another (I've seen this in other clues).
'colossus' becomes 'titan' (both can mean something very big).
'i' placed within 'titan' is 'TITIAN'.
'in' is the link.
(Other definitions for titian that I've seen before include "Reddish-gold; painter" , "Italian painter; hair colour" , "Venetian Renaissance painter" , "Painter; red tint" , "Painter of 16th century" .)