The Hellscape is one of my favorite things I have done while playing with the PV Tiles. The technique is very simple, but effective.
Start with a map using the plain gray cliff tiles and recoloring them to a dark color. Then Duplicate them and make the copy a bright color that works with the map. Making sure the dark copy is on top, use a patterned eraser to start erasing part of the dark cliffs, letting the colored ones show through.
A Recolor of the Lava texture and the red parts of the ground tiles allows creating an alternate version of this for an alternate version.
Zyph's Game Design 