In HotS second mission - ZLab02 - there's a strange thing with lighting. In the bottomleft part of map it's red, while in other parts it's normal at the same time. And I don't have an idea how it's done and how to copy it.
Its a new feature with the HoTs update. You don't need the expansion to use it fyi.
I haven't really used it, but there's a Lighting section in the Terrain layer where you can paint Lighting over your terrain. I reckon these mark areas of your map that are affected by a certain lighting.
When you have any window of the editor open, in the top bar where there's "File" and "Edit" and so on, go to "Window" and click on Lighting.
I believe it will by default pick the lighting used by your map, but I'm not 100% sure on this, so double check (I think default lighting is defined in the same place as your Terrain textures, fog color and so on, forgot the tabs name)
I also can't remember exactly which tab it was in the lighting editor, but it should be very obvious which one edits lighting regions (Since you'll be able to pick between 4 of them). You can then paint these regions onto the map in the terrain editor.
Another possible thing to do is create/edit another lighting set of its own, place a regular region in the terrain editor and then have a trigger switch the players lighting when he enters/leaves that region. (This changes the lighting for the entire map at once, so having a locked camera is probably best, which obviously won't really work in big RTS maps where the player has to look at multiple places, in which case you should definitely use lighting regions)
This method also breaks "Day of time" lighting (In the lighting window you can have it change lighting depending on the day of time and have it transition between things like day and night, have shadows move as time passes, etc. Changing lighting by trigger removes that functionality)