A red, one drunk by abstemious Scot (6)
I believe the answer is:
titian
'a red' is the definition.
(I know that titian is a type of red)
'one drunk by abstemious scot' is the wordplay.
'one' becomes 'I' (Roman numeral).
'drunk by' is an insertion indicator.
'abstemious' becomes 'tt' (I've seen this in other clues).
'scot' becomes 'ian'.
'i' inserted inside 'tt' is 'tit'.
'tit'+'ian'='TITIAN'
(Other definitions for titian that I've seen before include "He painted" , "Venetian artist" , "Venetian painter - shade of red" , "Painter of 16th century" , "Venetian Renaissance painter" .)