title: pheatmap: Color for NA
body: <p>Using R package pheatmap to draw heatmaps. Is there a way to assign a color to NAs in the input matrix? It seems NA gets colored in white by default.
  E.g.:</p>
  
  <pre><code>library(pheatmap)
  m&lt;- matrix(c(1:100), nrow= 10)
  m[1,1]&lt;- NA
  m[10,10]&lt;- NA
  pheatmap(m, cluster_rows=FALSE, cluster_cols=FALSE)
  </code></pre>
  
  <p>Thanks</p>