Help: can not change the color of polygon in function call?

Hi,
      I met a little trouble in changing the color of polygon in function call, which means that the black color of polygon can not be changed even if I changed the setting:
                        gsres@gsLineColor = "red"
      in the function "sub_draw_add".
         
      To simplify my problem, I write the following script (which is revised from http://www.ncl.ucar.edu/Applications/Scripts/xy_12.ncl ) in the end of the letter and the output eps figure is also attaced behind.

       Any suggestion and help is appriciated.

;*************************************************
; xy_12.ncl
;
; Concepts illustrated:
; - Emphasizing part of a curve in an XY plot
; - Drawing longitude labels on the X axis
;
;************************************************
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
;*******************************************
undef("sub_draw")
function sub_draw(wks,xaxis,index)
local wks,res,index,plot,xaxis
begin

  res = True ; plot mods desired
  res@tiYAxisString = "" ; add units to title
  res@tfPolyDrawOrder = "Predraw" ; put line on top
  res@tiMainString = "Highlight Part of a Line" ; title

  res@xyDashPatterns = (/0.,0./) ; keep all solid

  res@gsnFrame = False ; don't draw yet
  res@gsnDraw = False ; don't advance yet

  plot = gsn_csm_xy(wks,xaxis,index,res) ; create plot

return(plot)
end
;*******************************************
undef("sub_draw_add")
function sub_draw_add(wks,plot,xp,yp)
local plot,xp,yp,dname,dum
begin
;
; hight the line use p
;
   gsres = True ; poly res
   ;gsres@gsnFrame = False ; don't draw yet
   ;gsres@gsnDraw = False ; don't advance yet
   gsres@gsFillColor = True
   gsres@gsLineColor = "red" ; color chosen

   dum = gsn_add_polygon(wks,plot,xp,yp,gsres) ; draw polygon
   dname = unique_string("dum")
   plot@$dname$ = dum

return(plot)
end
;************************************************

begin
; read in netCDF file
;------------------------------------------------
  a = addfile("uv300.nc","r")
  u = a->U(0,:,{60})
  lat= a->lat

;
; First polygon
;...
  data = u({-60:-30})
  ndata= dimsizes(data)
  print(ndata)

  yp = new(ndata+1,typeof(data))
  yp(0:ndata-1) = u({-60:-30})
  yp(ndata) = yp(0)

  xp = new(ndata+1,typeof(lat))
  xp(0:ndata-1) = lat({-60:-30})
  xp(ndata) = xp(0)

 ;
 ; Second polygon
 ;...
  delete(data)
  delete(ndata)
  data = u({0:60})
  ndata = dimsizes(data)
  print(ndata)
  printVarSummary(data)

  yp2 = new(ndata+1,typeof(data))
  printVarSummary(yp2)
  printVarSummary(u({0:60}))
  yp2(0:ndata-1) = u({0:60})
  yp2(ndata) = yp2(0)

  xp2 = new(ndata+1,typeof(lat))
  xp2(0:ndata-1) = lat({0:60})
  xp2(ndata) = xp2(0)

;
; draw line
;...
  outname = "1"
  wks = gsn_open_wks("eps",outname)

  plot = sub_draw(wks,lat,u)

;
; draw polygon
;...

  plot=sub_draw_add(wks,plot,xp,yp)

  plot=sub_draw_add(wks,plot,xp2,yp2)

   draw(plot)
   frame(wks)
end

Li

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