Sphere.
https://commons.wikimedia.org/wiki/File:SRGB_gamut_within_CIELCH_color_space_isosurface_spherical.png
To do:
1. Make the axes and labels thicker and larger.
2. Offset the axes a bit from the actual x, y and z axes in order to
create some padding.
3. Make the axes dark gray instead of black.
Mike
