Under Map Options there is also a field affecting the fog of war used by the map.
Hidden means the terrain becomes hidden again once out of sight of player units plus the Reveal Radius. Expand means the vision of the terrain is not instant and it slowly grows determined by the Blend Speed. Color is the colour of the unexplored areas while the alpha is the brightness.
Also do not forget the Fog of War Color field under the Terrain Types data type.
0.962103634957463