you are alone in your mind because:
If you see the color red, and another person sees the color red, you both call out "red", but say the color red looks red to you, but to the other person, it looks like yellow. You could have no way of knowing how they saw that color, and you would just assume that you both saw the same thing. Both of you agree that it is the color red, but neither of you know how the other views it.