Once upon a time I played a map where you had to go into a teleport.
You were teleported into the xen world and suddenly everything
flashed into red. Sky, other solids and the players turned red. They were not fully red rendered as I could see the texture. It was like the whole map had become hell and soon everything became normal again in fade style. What was that? How could I do that? Only thing I can say is that it certainly was not env_fade!