I don't know about being happier as himself, but he certainly looks more like his old self, than he does No.6 now. But really we don't know what No.6's "old self " was. Being dressed like that at the Ball only makes him stand out from the crowd, even though the people at the Ball are in fancy dress. He would look even more out of place if everyone were in Village attire. As it is No.6 looks the round peg in a square hole!
Looking at it another way, its the same for the former No.2 when he first returns to London.
He can't go about London dressed like that, well he can, but a man of his reputation possibly working for the Foreign Office, but certainly within the Houses of Parliament, would look different, and stand out equally as much as the Prisoner does as himself in The Village. It's not until later that the former No.2 gains his old self.
As he returns to his former life, somewhere within the depths of the Establishment!
Be seeing you