Fogpal
Fogpal determines the color of the "visibility fog" EDuke32 draws on sectors.
Usage:
fogpal <palette> <red> <green> <blue>
For example the following values will give all sectors with the floor palette set to 1 a dark grey shade by default.
fogpal 1 12 12 12
You can then change the visibility level of the sector to your preferred amount to display a "fog" over the sector. In 3D mode of Mapster32, you can do this by holding down ALT and pressing + or - on the numpad to change the level. Holding down LEFT SHIFT while doing this will allow you to do smaller increment changes to the visibility of the sector.