title: R Heatmap color x-axis labels by group
body: <p>I am using the heatmap function to plot a matrix. Each column in the matrix represents one sample, and I have 4 sample types, each with a different quantity. Can I color the labels along the x-axis by sample type?</p>
  
  <pre><code>scaleyellowred &lt;- colorRampPalette(c("lightyellow", "red"), space = "rgb")(10)
  heatmap(fitted@H, Rowv = NA, Colv = NA, col = scaleyellowred)
  </code></pre>