This simulation is of 3-core percolation, with the normal choice of nearest neighbors on a square lattice. No sites are black because all sites have been culled; in fact, the critical density for this model is 1. The red/blue patterns indicate that in this model the seeds that eventually empty the lattice are rectangular voids.
Go here for an explanation of the correlated percolation model that generates this picture, and access to the correlated percolation applet.