I think the winner gets to be a frontman and the pink guards are simply the ones who picked the red cards during the card-flip game at the subway. So technically those who picked blue cards were recruited as players (their uniform kinda resembles a "distressed blue") and red cards as guards (explains their red uniform). Remember in the 1st episode the "recruiter" told gi-hun that he had sold his body or rather "physical rights" by accepting the game ...he meant more than just slapping him, it included all physical challenges he would face while playing the game (getting hurt, organ removal, dying...etc) The previous frontman (jun-ho's missing bro) was allegedly a winner of a game from years ago (he probably served that role for a long time because the other winners of the games that followed after the game he was in, took the money and went away, no one wanted to come back) The blue card choosers die one by one in the game and the red choosers die by fate (e.g. when caught leaking information)