https://commons.wikimedia.org/wiki/File:0_3d_60_75_v.png
https://commons.wikimedia.org/wiki/File:HSV_2D_profile_of_the_rainbow_gradient.png
https://commons.wikimedia.org/wiki/File:0_3d_60_75_v.png
c and gnuplot files
Better files
I have made hsv profile using finction from the gnuplot : see also https://gitlab.com/adammajewski/color_gradient#rainbow-colormap-or-sawtooth-rainbow-or-hsv
I have made demos fore reading gradient from the file
Feature request: palette