Materials need to be modeled for their physical properties. For example, if you're modeling heat flow you need to determine the heat-flow rates, which depend on dimensions as well as thermal conductivity, specific heat capacity, and mass density.
The appearance of materials also has to be modeled. This view-modeling is primitive in Heat-wave right now — the user can set 5 colors to use at 5 temperature levels. Intermediate temperatures are blends of these colors.
A more flexible approach would be to support model appearance options such as these: Transparent ( Glowing (GL_EMISSION) Mapped textures from bitmaps
Textures. Transparent materials. Glowing materials. Shininess. Diffuse, specular, and ambient components. Overlays showing isotherms (example of a highlight). Even bar charts showing the volumn of materials over temperature ranges. Lighting, essential for 3D drawing. But not for 2D. Many different drawing views, for 1D, 2D, 3D, and 4D models. Slicers, ways to highlight and obscure features. Lights: individual light sources pointing in different directions with varying brightness and colors. Ambient, diffuse, specular. .. You can go much farther with textured drawings.
Kind of a waste to encode height with both color and using the Z coordinate. Except not if temperature is the only thing you're looking at. Add isotherms and maybe even some fine gradient lines.