We're going to be producing a shader that must simulate two different materials; skin and water. (Or any other pair of materials would be handled similarly.)

To facilitate this, we'll find it very handy to use a mask - a pattern of white and black (or 1 and 0) that defines being in-segment versus out of segment.

This is really easy. We just magnify the height map and clamp it. I'll then use it to pick one of two colors for the surface.

Make a mask to define the area occupied by the line segment.

m = Clamp(50 * h)

Draw it as a displacement on a shiny orange surface

but make the segment a different color

color = Blend(ORANGE, .5 * GREEN, m)
s = Surface(color, .8, 1, 1, .02)
s.Displacement = .3 * h
 

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