问gnuplot虚线不以彩色绘制

EN

reset session
set term pngcairo dashed
set output 'dashcolor_1.png'
set label 1 "set style line 1 lt 2 lc rgb \"red\" lw 3" at -0.4, -0.25, 0 left norotate back textcolor rgb "red"  nopoint offset character 0, 0, 0
set label 2 "set style line 2 lt 2 lc rgb \"orange\" lw 2" at -0.4, -0.35, 0 left norotate back textcolor rgb "orange"  nopoint offset character 0, 0, 0
set label 3 "set style line 3 lt 2 lc rgb \"yellow\" lw 3" at -0.4, -0.45, 0 left norotate back textcolor rgb "yellow"  nopoint offset character 0, 0, 0
set label 4 "set style line 4 lt 2 lc rgb \"green\" lw 2" at -0.4, -0.55, 0 left norotate back textcolor rgb "green"  nopoint offset character 0, 0, 0
set label 5 "plot ... lt 1 lc 3 lw 3" at -0.4, -0.65, 0 left norotate back textcolor lt 3 nopoint offset character 0, 0, 0
set label 6 "plot ... lt 3 lc 3 lw 2" at -0.4, -0.75, 0 left norotate back textcolor lt 3 nopoint offset character 0, 0, 0
set label 7 "plot ... lt 5 lc 3 lw 3" at -0.4, -0.85, 0 left norotate back textcolor lt 3 nopoint offset character 0, 0, 0
set style line 1  linetype 2 linecolor rgb "red"  linewidth 3.000 pointtype 1 pointsize default
set style line 2  linetype 2 linecolor rgb "orange"  linewidth 2.000 pointtype 2 pointsize default
set style line 3  linetype 2 linecolor rgb "yellow"  linewidth 3.000 pointtype 3 pointsize default
set style line 4  linetype 2 linecolor rgb "green"  linewidth 2.000 pointtype 4 pointsize default
set noxtics
set noytics
set title "Independent colors and dot/dash styles" 
set xlabel "You will only see dashed lines if your current terminal setting permits it" 
set xrange [ -0.500000 : 3.50000 ] noreverse nowriteback
set yrange [ -1.00000 : 1.40000 ] noreverse nowriteback
set bmargin  7
unset colorbox
plot cos(x)     ls 1 title 'ls 1',        cos(x-.2)  ls 2 title 'ls 2',     cos(x-.4)  ls 3 title 'ls 3',     cos(x-.6)  ls 4 title 'ls 4',      cos(x-.8)  lt 1 lc 3 title 'lt 1 lc 3',       cos(x-1.)  lt 3 lc 3 title 'lt 3 lc 3',       cos(x-1.2) lt 5 lc 3 title 'lt 5 lc 3'