title: grayscale histogram with gnuplot
body: <p>I'm new to gnuplot and I want to draw a triple histogram for a set of data of any length.
  Here is my code but the line <code>set palette gray</code> seems to have no effect -- everything is still in RGB. What am I missing here?</p>
  
  <pre><code>set terminal pdf enhanced
  set output 'out.pdf'
  
  set palette gray
  
  set style data histogram
  set style histogram cluster gap 1
  
  set style fill solid 1
  set auto x
  set yrange [0:*]
  plot 'in.dat' using 2:xtic(1) title col, \
          '' using 3:xtic(1) title col, \
          '' using 4:xtic(1) title col
  </code></pre>