title: Fill area below a line in 3D with splot
body: <p>I am plotting a 3D 'fence plot' with multiple colors for each fence.  My sample data can be found here:</p>
  
  <p><a href="https://gist.github.com/anonymous/a926221ea96e92e86332" rel="nofollow noreferrer">https://gist.github.com/anonymous/a926221ea96e92e86332</a></p>
  
  <p>I plot this data using this:</p>
  
  <pre><code>colors = "red red red red red"
  splot for [i=1:words(colors)] 'input.sep.txt' index i u 2:1:3 w lines lc rgb word(colors,i)
  </code></pre>
  
  <p>The lines are drawn without issue, and I believe they are drawn correctly.  My question is this: how do I fill below the line so that it looks like a solid wall (i.e. all the way down to the 0 z value)? I tried using <code>w pm3d</code>, however this did not actually plot anything visible on the axis.</p>