plgcol0: Returns 8-bit RGB values for given color
from color map0 

DESCRIPTION:

    Returns 8-bit RGB values (-255) for given color from color map0 (see
    the PLplot documentation).	Values are negative if an invalid color id
    is given. 

SYNOPSIS:

plgcol0(icol0, r, g, b)

ARGUMENTS:

    icol0 (PLINT, input) :    Index of desired cmap0 color. 

    r (PLINT *, output) :    Pointer to 8-bit red value. 

    g (PLINT *, output) :    Pointer to 8-bit green value. 

    b (PLINT *, output) :    Pointer to 8-bit blue value.