title: change the background color of grid.arrange output
body: <p>I am using <code>grid.arrange</code> from <code>gridExtra</code> package to put two graphs on one page and save it to a png file. I like to change the background colour of the final png file that is produced by <code>grid.arrange</code>. Is it possible? I was not able to come across any info.</p>
  
  <pre><code>grid.arrange(p1, p2, main=textGrob("CPU Util", gp=gpar(cex=1.2, fontface="bold", col="#990000")), ncol = 1, clip=TRUE)
  </code></pre>