I don’t share your intuition here. I think many people would see blue as the “band together” option and would have confidence that others will do the same. For the average responder, the question would reduce to “choose blue to signal trust in humanity, choose red to signal selfish cowardice”.
“Innate faith in human compassion, especially in a crisis” is the co-ordination mechanism, and I think there is pretty strong support for that notion if you look at how we respond to crises in real life and how we depict them in fiction. That is the narrative we tell ourselves at least, but narrative is what’s important here.
I would be surprised if blue was less than 30%, and would predict around 60%.
No matter what the game theory says, a non-zero number of people will choose blue and thus die under this equilibrium. This fact—that getting to >50% blue is the only way to save absolutely everyone—is enough for me to consider choosing blue and hope that others reason the same (which, in a self-fulfilling way, strengthens the case for choosing blue).