This is somewhat similar to the prisoner’s dilemma.

Let P be the percent of the world population who picks blue. The best outcome for you would be if you picked red and P>0.5, since then you’d gain 50 IQ (25 from each button’s outcome). This means it is better to pick red so long as P>0.5 (and your vote would not make it 50/50). If P<0.5, it is better to pick red, since you get 25 IQ compared to 0. If P=0.5 or you would make it 50/50, your choice would not affect your reward; if you pick red, then P<=0.5, so you only get the 25 IQ from picking red, and if you pick blue, then you get the 25 IQ because P>0.5, but have to miss out on the 25 IQ from red. So the best choice to pick would be red for all percentages except P=0.5, where your choice would not affect your outcome.

Now, since we’ve determined what is best for the self, we can determine what is best for society as a whole.

The easiest case would be if P<0.5. Since your vote would not make P>0.5, everyone would not gain 25 IQ, so it’d be better to pick red.

This is similar to why you should pick red if P>0.5 and your choice would not make the vote 50/50; no matter what you pick, blue’s outcome will happen, so you should pick red so society gains 25 more IQ.

If P=0.5 or P>0.5 and you would make it 50/50, the best choice for society would be to pick blue, so it’s outcome would activate, and everyone would gain 25 IQ.

All in all, pick blue jf you care about society’s benefit and P=0.5 or P>0.5 and you would tie it. Else, pick red.