title: How can I use different color palettes for different layers in ggplot2?
body: <p>Is it possible to plot two sets of data on the same plot, but use different color palettes for each set?</p>
  
  <pre><code>testdf &lt;- data.frame( x = rnorm(100), 
                    y1 = rnorm(100, mean = 0, sd = 1), 
                    y2 = rnorm(100, mean = 10, sd = 1),
                    yc = rnorm(100, mean = 0, sd = 3))
  ggplot(testdf, aes(x, y1, colour = yc)) + geom_point() +
    geom_point(aes(y = y2))
  </code></pre>
  
  <p>What I would like to see is one set of data, say <code>y1</code>, in blues (color set by <code>yc</code>), and the other set in reds (again color set by <code>yc</code>).</p>
  
  <p>The legend should then show 2 color scales, one in blue, the other red.</p>
  
  <p>Thanks for your suggestions.</p>