Two graphs are shown in the simulation, one showing the spring potential energy and the other showing the block's kinetic energy.

Which graph is which?

1. The red one is the kinetic energy; the blue one is the potential energy
2. The blue one is the kinetic energy; the red one is the potential energy
3. The graphs are interchangable so you can't tell which is which

The blue graph is zero when the block turns around (v = 0) and it peaks when the block passes through the equilibrium position (maximum speed) so it must be the kinetic energy.