Think about these questions!
Assuming that the green ball on the left and the blue ball in the middle are identical except for their color, how would their potential energy compare? Why do you think this?
How do you know that the blue ball on the right has more potential energy than the blue ball on the left? Where did the additional energy come from?
If the person were to release the blue ball above his/her head, what would happen to its potential energy? How could you test your idea?