title: Use AsIs color in ggplot chart
body: <p>I was looking at <a href="https://stackoverflow.com/questions/7570319/the-right-way-to-plot-multiple-y-values-as-separate-lines-with-ggplot2">The right way to plot multiple y values as separate lines with ggplot2</a> to get the proper syntax to have multiple Y's for the same X. I was able to do so correctly (in this case I actually used the format of the submitter, as I only wanted one extra Y so it was just as easy).</p>
  
  <p>My trouble comes in that I want to set the two lines to different colors, and I want to specify the color (ie. <code>color = I('blue')</code>), but doing so results in the error </p>
  
  <p><code>Don't know how to automatically pick scale for object of type AsIs. Defaulting to continuous
  Error: Discrete value supplied to continuous scale</code></p>
  
  <p>My code as is follows:</p>
  
  <pre><code>ggplot(aes(x = age), data = by_age) +
    geom_line(aes(y = friend_mean, color = "blue")) +
    geom_line(aes(y = friend_med))
  </code></pre>
  
  <p>This does result in one line being colored, but not in the color specified, and it applies <code>"blue"</code> as a label. </p>
  
  <p>So how would I go about setting a color in ggplot, using defined, static colors (red, blue, green, etc.)?</p>
  
  <p>Thanks!</p>