Wine, dry white ultimately? It’s for one in the party (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

ROSÉ(a light pink wine) + TT(abbrev. for “teetotal/abstaining from alcohol/dry) + last letter of ( … ultimately ) “ white ”. Defn: A decoration worn by a supporter or member of, say, a political party.