The fog is supposed to block your vision, so you don't know what is around you until you dig in that direction. However, if you move the camera around rapidly, the game doesn't render the fog for a frame or two on the "new area" that you've just scrolled into.
EDIT: This only works if you scroll Upwards or to the Right. Down and Left work as intended
EDIT 2: This seems to work best if the colony has just started. Even a couple of minutes in the revealed sections become smaller.
Hold right click or middle mouse button to control the camera, and then quickly scroll into the black fog.