DKRZ NCL xy-plot example coloring between lines

Example script:

;--------------------------------------------------------------------
; DKRZ NCL example: NCL_transparent_filled_curves.ncl
;
; Description: Use dummy data.
;              Draw two curves with 'pseudo standard deviations' and
;              fill the areas between the lines with colors. Use
;              transparency to make the underlying curve visible.
;
; 01.03.18 kmf
;--------------------------------------------------------------------
begin

;-- compute test data for two curves with 'pseudo stddev'
 x = ispan(-50,50,1)

 y1 = sin(0.05*x)
 ystdp1 = y1 + 0.4
 ystdm1 = y1 - 0.4

 y2 = sin(0.07*x)
 ystdp2 = y2 + 0.3
 ystdm2 = y2 - 0.3

;-- set colors
 cdsg0 = (/0.2,0.3,0.3,0.5/) ;-- darkslategray
 cdsg1 = (/0.6,1.0,1.0,0.5/) ;-- darkslategray1
 cblack = (/0.0,0.0,0.0,0.5/)
 cgray = (/0.3,0.3,0.3,0.5/)

;-- set above, below and line colors for both curves
 belowcols1 = (/cdsg0,cdsg0/)
 belowcols2 = (/cdsg1,cdsg1/)
 abovecols1 = belowcols1
 abovecols2 = belowcols2

;-- line settings
 linecol1 = cgray ;-- line color 1st curve
 linecol2 = cblack ;-- line color 2nd curve
 linepattern1 = 0 ;-- line dash pattern 1st curve
 linepattern2 = 14 ;-- line dash pattern 2nd curve
 linewidth = (/1,5,1/) ;-- linewidth (lower, middle, upper)

;-- open workstation
 wks_type = "png"
 wks_type@wkWidth = 1200
 wks_type@wkHeight = 1200
 wks = gsn_open_wks(wks_type,"plot_transparent_filled_curves")

;-- set resources
 res = True
 res@gsnDraw = False ;-- don't draw the plots, yet
 res@gsnFrame = False ;-- don't advance the frame
 res@gsnMaximize = True ;-- maximize the plot

 res@xyMonoDashPattern = True ;-- use a solid lines for all curves
 res@xyDashPattern = linepattern1 ;-- line pattern
 res@xyLineThicknesses = linewidth ;-- line width
 res@xyLineColor = linecol1 ;-- line color
 res@gsnXYBelowFillColors = belowcols1 ;-- use color between below lines
 res@gsnXYAboveFillColors = abovecols1 ;-- use color between above lines

 res@trYMinF = -1.5 ;-- y-axis minimum
 res@trYMaxF = 1.5 ;-- y-axis maximum

;-- define data arrays for both curves and plot them
;-- first plot
 data1 = (/ystdm1, y1, ystdp1/)
 plot1 = gsn_csm_xy(wks,x,data1,res)

 res@xyLineColor = linecol2 ;-- line color
 res@xyDashPattern = linepattern2 ;-- line pattern
 res@gsnXYBelowFillColors = belowcols2 ;-- use color between below lines
 res@gsnXYAboveFillColors = abovecols2 ;-- use color between above lines

;-- second plot
 data2 = (/ystdm2, y2, ystdp2/)
 plot2 = gsn_csm_xy(wks,x,data2,res)

;-- overlay both plots
 overlay(plot1,plot2)

;-- draw the plot and advance the frame
 draw(plot1)
 frame(wks)

end

Result: