This is the same as preset 3 except, in addition to the display of the electrons on the right, we have displayed on the left the positions, with the k's reversed, of the UNOCCUPIED states. That is, if the state k on the right is unoccupied, then on the left a white dot is put on the state -k. (See the discussion of holes in Kittel for the rationale.)
Run briefly and stop. In the right-hand display find an empty state which is clearly below the Fermi surface. Call its k-value k1. Find the point in the left-hand display with k-value equal to -k1. It should be shown as occupied by a "hole".
Remember that we can shift pieces of the dispersion relation around by reciprocal lattice vectors without altering the physics. If you click the shift origin toggle, "peierls" does this with pieces of the zone, assembling the four quadrants of the zone to share the four (originally) exterior corners. This shared corner is displayed at the center of the field. The blue lines remain the boundaries of the original first Brillouin zone.
Now ignore the picture on the right, focus on the left, and run a little longer to see what happens. Suppose you were to construct a Sommerfeld picture for particles with positive charge and positive mass. How would they respond to an electric field?