为什么gauss做出来的图背景色是黑色呢？请问如何修改呢？
程序如下：/*
** STDPLOT.e
** Construct plots of daily stock index returns as shown in Figure 1.1
**
** Written by Dick van Dijk
** Last revision on May 20, 1999
**
*/

new;
cls;
library pgraph;
__maxvec=400000;

graphset;
_pdate="";
_pcolor=15;
_plctrl=0;
_psymsiz=1;
_pnum=1~2;
sz=.2;
_pnumht=sz;
_paxht=sz;
_pmargin=0~0.1~0.0~0.15;
xlabel("Time");
dataset="STINDDL";
y=loadd(dataset);
vnames=getname(dataset);
nos=rows(vnames);
n=rows(y);
_pysci=6;

i=0;
do until (i==nos);
  i=i+1;

  _ptek="STDPLOT" $+ ftocv(i,1,0) $+ ".tkf";

  x=seqa(1,1,n);
  let chx="1/86" "1/88" "1/90" "1/92" "1/94" "1/96" "1/98";
  chy=0;
  asclabel(chx,chy);

  begwind;
  window(2,1,1)
  /* Draw the graphs */
  scale(x,y[.,i]);
  xtics(-4,n,522,2);
  ylabel("P\]t\[");
  xy(x,y[.,i]);
  nextwind;

  ry=100*(ln(y[2:n,i])-ln(y[1:n-1,i]));

  scale(x,ry);
  xtics(-4,n,522,2);
  ylabel("y\]t\[");
  xy(x[2:n],ry);
  endwind;
endo;
图如下：