Colossus pocketed single red (6)
I believe the answer is:
titian
'red' is the definition.
(I've seen this before)
'colossus pocketed single' is the wordplay.
'colossus' becomes 'titan' (both can mean something very big).
'pocketed' is an insertion indicator (pocket can mean to steal or take).
'single' becomes 'I' (one).
'titan' enclosing 'i' is 'TITIAN'.
(Other definitions for titian that I've seen before include "Italian painter; hair colour" , "Italian 16th-century painter" , "It. painter, famous for redheads" , "Painter of 16th century" , "Italian artist" .)