title: How to change heatmap.2 color range in R?
body: <p>I'm using gplot to produce a heatmap showing log2-fold changes of a treatment groups versus paired controls. With the following code:</p>
  
  <pre><code> heatmap.2(as.matrix(SeqCountTable), col=redgreen(75), 
             density.info="none", trace="none", dendrogram=c("row"), 
              symm=F,symkey=T,symbreaks=T, scale="none") 
  </code></pre>
  
  <p>I output a heat map with real fold change values (i.e., non Row-Z score) which is what I'm after, in the Red-Black-Green color scheme that is every biologist's favorite!</p>
  
  <p><img src="https://i.stack.imgur.com/uhFbP.jpg" alt="http://i.stack.imgur.com/uhFbP.jpg"></p>
  
  <p>The actual range of log2-fold change is -3/+7, with many values in the -2/-1 and +1/+2 range, which appear as dark red/green (respectively). This makes the whole heatmap quite dark and so difficult to interpret. </p>
  
  <ul>
  <li>Is there a way of skewing the color gradient to make it less linear? That is, so that the gradient from black to quite bright occurs over a smaller range? </li>
  <li>And / or change the color range to be asymmetric, i.e., to run from -3/+7, as the data does, rather than -7/+7 as the scale currently does, with black still centered on zero? </li>
  </ul>