The three pieces and 6 buttons continue to prevail for Mr. Thompson. He first appeared in a green checkerboard patterned number. For those who care to note the details his nearly constant use of a boutonnierre (oft a rose) should not be ignored. Nowadays they seem to be strictly reserved for more formal or special occasions (a rose is considered the most formal flower, I believe) and if a politician were to wear one I have no doubt that the press would admonish him.
Another detail that should not be overlooked is how Nucky wears his six button vests, that is, with all buttons buttoned. Convention dictates that only five should be buttoned, leaving the sixth unbuttoned. Although I do not know the exact date that it became proper to do so, I do believe that it started prior to the time period Boardwalk Empire is set in (I will delve into the history of this at a later time). If this is true then I am not sure as to the reason why he keeps all six buttoned, but then again, this could be something that is beyond my knowledge. Either way, Nucky Thompson for President 2012.