1.) The pure form where the button presses and restricted to legal agents (i.e. people with credible legal standing over their choices). 2.) The mixed form with the caveat listed here inclusive of all humans whether they are even physically capable of pushing a button. 3.) you could also go for a more expansive scenario that takes 2 to the extreme and includes animals as well.
1.) gets to the game theoretic form of the question. 2 muddies things, and 3 sets up a case for blue since the non agentic voters asymptote to 50-50 and a slim edge is morally preferable to killing half.