color_index, hue, lightness, saturation
Change the color of a PGPLOT color index (HLS version).

PARAMETERS
----------

color_index  -  The PGPLOT color index to be modified.

hue          -  The color as an angle on the Hue-lightness-saturation
                diagram. Blue is at 0, red at 120 and green at 240
                degrees.

lightness    -  How white the color appears 0 -> 1.

saturation   -  The color purity. 0 is gray. 1 is pure color.

RELATED COMMANDS
----------------
pgscr  - Change the color of a PGPLOT color index (RGB version).
pgscrn - Set the color of a PGPLOT color index by name.