Sorry spec24 I misunderstood partially,
the actual blackness throughout the game level is only available in game. Both as GM and in editor (both editor and game mode) that fog is disabled.
As a player in-game it should be fine though, as long as it is enabled in the Level Data as mentioned earlier. Were you able to test that already?
Ok, in the editor, if I reload my level and hit the "switch game/editor" button I get fog of war (though it's a really large radius... any way to reduce that?). So I saved the level and prepared a new campaign in GM mode, adding the newly saved level. I then started up a client version running on the same computer to test the level. No luck. Fog of war is non-existent on the client side. I closed both programs and opened the level back up in the editor. Fog of war appears with the "switch game/editor" button as expected