title: Choosing line type and color in Gnuplot 4.0
body: <p>I have two pairs of datasets, which I need to plot using Gnuplot.</p>
  
  <p>I want the first pair to be plotted in red, one solid and one dashed. The second pair, I want to plot in blue, one solid and one dashed.</p>
  
  <p>I've experimented with <code>set style line</code> several times, but I cannot get this exact behaviour. My last attempt (attached) plots the first pair in red (solid) and the second pair in blue (dotted).</p>
  
  <p>Any help will be greatly appreciated.</p>
  
  <pre><code>set style line 1 lt 1 lw 3 pt 3
  set style line 2 lt 1 lw 3 pt 3
  set style line 3 lt 3 lw 3 pt 3
  set style line 4 lt 3 lw 3 pt 3
  plot 'data1.dat' using 1:3 w l ls 1,\
       'data1.dat' using 1:4 w l ls 2,\
       'data2.dat' using 1:3 w l ls 3,\
       'data2.dat' using 1:4 w l ls 4
  </code></pre>