Let's be logically consistent
Your vote has an incredibly tiny chance of actually making any difference, being the deciding vote. It doesn't feel like it, but that chance stays the same no matter what percentage of votes blue needs to win. It can be 50/75/25/95/5 percent, doesn't matter. Your vote always has the same level of impact.
So if you choose red but say that you'd choose blue if the threshold for blue winning was low enough, you are basically saying that you'd virtue signal, even if only to yourself, if it was safe enough. You aren't consistently following rational self-interest, that demands you press red unless blue can win with a single vote.
And if you choose blue but say that you'd choose red if the threshold for blue winning too high, you are basically saying that you are choosing blue because it makes you feel good about yourself while not risking anything since you are sure it'll win. You aren't consistently following rational altruism, that demands you press blue no matter how high the threshold is to achieve the best possible result.
So choose one button. Decide what is more important to you, genuine self-interest or genuine altruism.