Fog of war
The fog of war decides which tiles a player starts the game unable to see. Every player has their own, and a map that carries no fog data at all starts fully fogged — which is what a new map does, and what the editor draws until the first stroke.

Select any of the eight players at the top of the palette and every stroke and fill edits all of them at once; View picks whose fog the map and minimap show. Fog and Clear are the brush modes, Shift-drag paints the opposite, and Alt+click picks up which players have fog on a tile. Fog All, Clear All, Invert and Copy Fog act on the whole map for the selected players.
Fogged tiles darken over everything, units and locations included, in the tint the game itself uses for that tileset.