title: Fill a polygon with gradient color along a certain direction
body: <p>I am trying to fill a polygon with a gradient color from red-to-blue and blue-to-red. </p>
  
  <p>I tried using fill and colormaps but they don't work.</p>
  
  <pre><code>x0 = [0  0   63   63   58   58   82   82   77  77  140 140];
  y0 = [0 -14 -14 -374 -374 -398 -398 -374 -374 -14  -14  0 ];
  figure;
  plot(x0, y0,'-k','linewidth',2); hold on all;
  h1=patch(x0, y0,'r');
  </code></pre>
  
  <p>Anyone can help to get this blue at the top and red at the bottom (and other way around, red at the top and blue at the bottom, as the colors gradually change in between)?</p>