mfpic-doc.pdf.

4.3 COLORS IN MFPIC. 28
The first two commands are never necessary in early METAPOST, but they are still defined: they
simply return the given color if it is a known argument of type color, or apply the function gray()
is it is numeric, and return black for an unknown name.
The last one makegray converts any color to a numeric, and then returns either that number
(recent METAPOST) or that multiple of white (early METAPOST). In METAFONT, all three pass the
(presumably numeric) argument 〈clr〉 unchanged.
All three functions return some version of black if 〈clr〉 is not a color of some type, or has an
unknown value.
4.3.2 ESTABLISHING MFPIC DEFAULT COLORS
\drawcolor[〈model〉]{〈colorspec〉}
\fillcolor[〈model〉]{〈colorspec〉}
\hatchcolor[〈model〉]{〈colorspec〉}
\pointcolor[〈model〉]{〈colorspec〉}
\headcolor[〈model〉]{〈colorspec〉}
\tlabelcolor[〈model〉]{〈colorspec〉}
\backgroundcolor[〈model〉]{〈colorspec〉}
These macros set the default color for various drawing elements. Any curve (with one exception,
those drawn by \plotdata), whether solid, dashed, dotted, or plotted in symbols, will be in the color
set by \drawcolor. Set the color used by \gfill with \fillcolor. For all the hatching commands
use \hatchcolor. For the \point, and \plotsymbol commands, as well as \gridpoints and
\plrgridpoints, use \pointcolor, and for arrowheads, \headcolor. One can set the color used
by \gclear with \backgroundcolor (the same color will also be used in the interior of unfilled
points that are drawn with \point) and, when mplabels is in effect, the color of labels can be set
with \tlabelcolor.
The optional 〈model〉 may be one of rgb, RGB, cmyk, gray, and named. The 〈colorspec〉 depends
on the model, as outlined below. Each of these commands sets a corresponding METAPOST color
variable with the same name (except \backgroundcolor sets the color named background). Thus,
after drawcolor has been set, one can issue the command \fillcolor{drawcolor} to fill with
the same color.
As previously discussed, all these colors are initially set to black except background is set to
white.
If the optional 〈model〉 argument is omitted, the color specification may be any expression recognized
as a color by METAPOST. It is highly recommended (for portability) that one use either a
predefined name or one of the color functions of the previous section.
When the optional 〈model〉 is specified in the color setting commands, it determines the format
of the color specification as in figure 1.
Model:
rgb
RGB
cmyk
gray
named
Specification:
Three numbers in the range 0 to 1 separated by commas.
Three numbers in the range 0 to 255 separated by commas.
Four numbers in the range 0 to 1 separated by commas.
One number in the range 0 to 1, with 0 indicating black, 1 white.
A METAPOST color variable name either predefined by MFPIC or by the user.
Figure 1: Color specifications