Im not sure if other people have mentioned this idea, but I think visualizing terrain and slopes could be handled similarly to topographic maps. Instead of using a line where there is a increase of height you could have that each elevation be one solid shade of a the background color. The lower the terrain is to sea level, the darker the shade, and lighter it gets the higher it gets. an additional idea would be to have a customization option for how many elevations changes there are on a map. example: 10 shades or 5, etc. Random would simply pick a number between 1-20.