This is the "normalised 8 bands rainbow". There are lot of "specmap"
designed mostly for special 3D color effects and image processing.
Smath is not happy vectorising linterp(,,,). Done piecewise for
demo and export the rainbow band, enjoy.

Jean

Image Rainbow Colormap.sm (168 KiB) downloaded 58 time(s).

See also this link. This is a demonstration of color coded plots with the standard plot region in SMath.