color of his own hat.
person 2 knows that if his hat was red, person 3 would see that both person 1's hat and person 2's hat were red, therefore, person 3's hat would have to be blue. person 3 cannot know the color of his own hat.
since person 1's hat is red, person 2's hat must be blue.
i got the same result but not for as good of a reason.
person 1 and person 4 have no idea what color anyone's hats are so they won't guess.
person 3 knows person 1's hat is red and person 2's hat is blue so there's still a 50% chance his hat is either color.
person 