Everyone knows who the Browncoats were: volunteers who fought for their independence against the Alliance, known for their trademark brown leather dusters like Malcolm Reynold's.
In my campaign, there were also Blackjacks, they were the members of the Independents Space Navy. The core of the ISN came from Londinium with the LSN Glory, a battlecruiser that defected with most of her crew on the eve of the war. The black uniform jacket of the former Londinium Space Navy became the accepted style of the crews of ships fighting the Alliance.

(Gamemaster's note: I suppose a big part of the name was that I was reading Jack Campbell's Lost Fleet series at the time. His main character is a naval officer named John "Black Jack" Geary…)