Using the add-on utility "CADstudio DTMcolSl" (free) you can automatically color your topographic digital terrain model (DTM) consisting of triangular 3DFACEs by its slope.
Just download www.cadstudio.cz/download, load it with APPLOAD and start the DTMCOLSL command. Select your model (or All) and choose one of the predefined color palettes (16-color, 256-color, rainbow, big rainbow, green, land, hydro or pastel colors). The tool will analyze the extreme slopes (minimum, maximum), calculates the color ramps and then the toposurface 3D model will be recolored automatically. You can limit the range of slopes - the parameter „range offset“ adjusts the palette range – you can narrow the coloring range by NN%.
See examples of the DTMcolSl results:
See also the DTMcol utility - for elevations.
You can get similar results from the surfaces functionality in AutoCAD Civil 3D