Low density gas is blue and transparent and high density gas is red and opaque in the display. The highest density "knots" occur at the intersection of filaments and correspond to clusters of galaxies in the simulation.
This simulation uses a mixture of hot and cold dark matter. Here are further details of the calculation.
Usage: Use the "Play" button and "Stop" button to control play. When stopped, "Back" steps back one step and "Step" steps forward one step. "Home" returns to the beginning from any point.