Yes, A basic one.
When you open map or create one. You may choose the hidden mode. That means the fog will cover the whole map.
In rolisteam, you may select 4 color modes:
Normal : to paint anything (line, rectangle round ....)
Erase: to erase anything (painted with normal mode)
Veil: to paint anything (line, rectangle round ....) as Fog of war. So you will paint the fog of war.
Unveil: to erase anything on the fog of war.
You must understand that it is color mode and then you can select any tool to paint this color.
To trigger, each mode you have to :
-Normal: select any color
-Erase: select the erase (red cross on white background) tool button
-Veil : select the black square with white triangle button
-unveil: select the black square with black triangle button.