title: Visible spectrum with gnuplot
body: <p>So I have this kind of data </p>
  
  <pre><code>3.500E2 -0.956862
  ...
  10.00E2 -1.95941
  </code></pre>
  
  <p>in a file.</p>
  
  <p>If I plot it it looks like this:</p>
  
  <p><img src="https://i.stack.imgur.com/p3LSl.png" alt="gnuplot graph with line"></p>
  
  <p>Now I want the area under the curve filled with the visible spectrum, like this: </p>
  
  <p><img src="https://i.stack.imgur.com/wgKrD.png" alt="filled curve with visible spectrum"></p>
  
  <p>I already found <a href="http://comp.graphics.apps.gnuplot.narkive.com/tWIXsyfH/gnuplot-visible-light-spectrum-palette" rel="noreferrer">this forum post</a>, which draws me a nice visible spectrum, but I can't further add my own curve into it, as this appears to be a pm3d plot.</p>
  
  <p>What can I do?</p>