The exact style of display depends on the user interface and on user preferences, but for some games, you may want to encourage a particular style by making it be the default.
GlobalVariable: unseen-char str
This variable is a string whose first character will be used to
represent unexplored terrain.
If the string consists of two characters, the second char will be
scattered throughout a field of the first char.
Defaults to "".
GlobalVariable: unseen-color str
This variable is the name of a color that will be used to
represent unexplored terrain.
Defaults to "".
GlobalVariable: unseen-image-name str
This variable is the name of an image that will be used to
represent unexplored terrain.
Defaults to "".
GlobalVariable: grid-color str
This variable is the name of a color to use to draw the
cell-separating grid.
Defaults to "".