For it to be murder it would need to be unlawful (lets just assume this entire hypothetical is unlawful) and planned, so unless red pressers are specifically doing it to kill blue pressers it is factually not murder. Blue pressers have put themselves into the situation of possibly dying, which was entirely their choice and isn't the responsibility of anybody else (ignoring the "forced to press a button by some mystical force/being").
There is a reason why even "duty to rescue" laws usually do not require the rescuer to endanger themselves doing it, which in this case would most certainly be the case (going from 0% of death to "who knows, this is entirely out of my control but non-negligable chance of dying" % of death).
> If they just built tracks and started running trains on them without taking measures to avoid mowing people down they absolutely would be guilty of murder.
Most stations in the world do not have any guardrails to the tracks themselves. If someone decides to walk onto them as the early end of a station they will most likely die if the train is arriving. The tracks were there, the train was scheduled just the person decided to put themselves into harms way. At most it would be considered manslaughter.
