title: is there a way to change the color palette for GGally::ggpairs using ggplot?
body: <p>I would like to change the color palette for the <code>GGally</code> function <code>ggpairs</code>.  When I attempt to add ggplot commands to the ggplot returned using <code>getPlot</code>, the colors do not change.</p>
  
  <pre><code>my_pair_plot = ggpairs(dataset, color="var1")
  getPlot(my_pair_plot,2,1) + scale_fill_brewer(palette = "Set2")
  </code></pre>
  
  <p>Attempting to put ggplot commands directly on the <code>ggpairs</code> function results in an error.</p>
  
  <pre><code>ggpairs(dataset, color="var1") + scale_fill_brewer(palette = "Set2")
  </code></pre>