There are 25 colors available for PENS. Colors -1, 0 and 7 are SPE-
CIAL, colors 1 to 6 are FIXED (named colors or their equivalent shade of
grey on grayscale terminals). The last 16 are user-defined.
Color 0 (the default for the default PEN 0) is ALWAYS the foreground
color (i.e., always visible whatever the background color of the graphic
window is), and becomes BLACK on the paper hardcopy. Color 7 is ALWAYS
the background color, useful for text written on an grey-scale image for
Colors 1 to 6 are defined as follows for a standard display with suffi-
cient colors available in its colormap:
"red","green","blue","cyan","yellow" and "magenta"
For grey-scale displays, it becomes:
"grey42","grey70","grey14","grey28","grey56" and "grey84"
This may vary depending on the number of available colors on your dis-
The last 16 colors are user-definable (see HELP LUT) and correspond to
the 16 'FILL PENS' used as fill colors in various commands, like
RGMAP /GREY or POLYGON /FILL.
Finally, the color -1 is negative, which means it will have an inverse
color of what is behind. It is useful to draw segments which are always
visible, whatever the context. This special color is available only un-
der X and PNG devices. For the others, the foreground color (0) is used.