color_index, red, green, blue
Change the color of a PGPLOT color index (RGB version).

PARAMETERS
----------

color_index   -   The color index to be changed. See 'help pgsci'
                  for the standard assignments.

red           -   The red contribution to the color:
                   0 - Black.
                   1 - 100% red.

green         -   The green contribution to the color:
                   0 - Black.
                   1 - 100% green.

blue          -   The blue contribution to the color:
                   0 - Black.
                   1 - 100% blue.

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