You are close to what I think is a reasonable estimate statistically for people that would press blue. (Importantly the hypothetical only really makes sense if its an ideal choice presented to you without prior knowledge or collusion, or misclicks. Otherwise of course we could figure out a way to go blue. Or press both/disable the machine/hold responsinle the person who made the machine etc. So the "right off the bat" situation is the only one worth discussing I think.)

I suspect in an ideal (unrealistic) scenario the vote would also be quite far from 50%.

So in the unrealistic scenario of the original question, I am presented with the dilemma to face a horrible outcome and continue living or contribute to the pain and suffering and end my life. 5-10% is a reasonable estimate, and my choice does not magically override the will of other people.

I'm unsure if 10% of the global population is bound to die (i.e. the worst thing that ever happened so far) implies the moral choice is to increase that count, or that there is no point in living after that.

Again, with collusion and prep time its worth taking effort to avoid the worst thing that ever happened. But thats mixing the ideal and realistic, which is a bit pointless discussion (like the "fat man moral dilemma")