Transparent Filled Polygon GNUPLOT

#!/usr/bin/perl

########## PLOT#############################################
open my $GP, '|-', 'gnuplot -persist';
print {$GP}  <<'__GNUPLOT__';
set xlabel "XCORD_CELL_CENTER"
set ylabel "YCORD_CELL_CENTER"
set format y "%s";
set size ratio -1
set tics font ", 6"
set ytics 3180000,10000,3280000
set xrange [706017:780000]
set yrange [3180000:3280000]
set style fill transparent solid 0.5 
plot 'polygon1.txt' using 1:2 w filledcurve above lt 1 lc rgb "forest-green" t '','polygon2.txt' using 1:2 w filledcurve above lt 1 lc rgb "gold"  t '', 'polygon3.txt' using 1:2 w filledcurve above lt 1 lc rgb "dark-violet"  t '' ;

__GNUPLOT__

close $GP;