Syntax: CTYPE WORD
or      CTYPE INTEGER
or      CTYPE = expr

  The CTYPE WORD sets the line colour (American: color) to be WORD, if
your display device supports coloured lines. Initially, WORD must be
one of the names "default", "white", "black", "red", "green", "blue",
"cyan", "magenta", or "yellow".  Each device chooses a value for
"default" (e.g.  white for Xwindows, black for sunwindows).

  Initially, CTYPE INTEGER is another way of selecting the same
colours as are available with CTYPE WORD, where the INTEGER is an
index into the array [ default, white, black, red, green, blue,
cyan, magenta, yellow ] so CTYPE 1 is the same as CTYPE white.
However, the CTYPE = expr command redefines the available colours to
be the elements of the array given by expr. If it is arithmetic, each
element of this array is interpreted as RED + 256*GREEN + 256^2*BLUE.
If it is string-valued, the elements of the vector give the names that
you can use to refer to the colours.  You should not try to modify the
value of default with CTYPE = expr, as it will be reset when you
change devices.

  You can get the current CTYPEs back as vectors with the expressions
CTYPE() (for red + 256*green + 256^2*blue) or CTYPE(STRING) for their
names.