Syntax: CTYPE WORD
or      CTYPE INTEGER
or      CTYPE = expr

  The CTYPE WORD sets the line colour to be WORD, if your display
device supports coloured lines. 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. Each element of this array
is interpreted as RED + 256*GREEN + 256^2*BLUE. You should not try to
modify the value of default with CTYPE = expr, as it will be reset
when you change devices.