title: two different scale_colour_gradient2() for different lines in ggplot2
body: <p>Base Model: <a href="https://www.dropbox.com/s/jhp2g4n89grhwi6/pr_base.RData?dl=0" rel="nofollow noreferrer">https://www.dropbox.com/s/jhp2g4n89grhwi6/pr_base.RData?dl=0</a></p>
  
  <p>Opt Model: <a href="https://www.dropbox.com/s/0mdupo1ryi4a7o3/pr.RData?dl=0" rel="nofollow noreferrer">https://www.dropbox.com/s/0mdupo1ryi4a7o3/pr.RData?dl=0</a></p>
  
  <p>I have saved them as (base model = pr_base) and (optimial model = pr) - pr being precision recall.</p>
  
  <p>I have plotted them as a <code>ggplot</code> using the following code:</p>
  
  <pre><code>pr &lt;-  readRDS("pr.rds")
  pr_base &lt;- readRDS("pr_base.rds")
  
  
  
  ggplot() +
    geom_line(data = data.frame(pr$curve), aes(x = X1, y = X2, color = X3)) +
    geom_line(data = data.frame(pr_base$curve), aes(x = X1, y = X2, color = X3)) +
    labs(x = "r",y = "p", title = "prc", colour = "legend") +
    scale_colour_gradient2(low = "white", mid = "grey", high = "black")
  </code></pre>
  
  <p>What I am trying to do is to reverse the scales / colours for the two models, to have the first <code>geom_line</code> as a white to black scale and the second <code>geom_line</code> as a black to white scale in order to differenciate them. (ignore the AUPRC in the image). At the moment they are both white - black scales.</p>
  
  <p><a href="https://i.stack.imgur.com/2Uxq9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2Uxq9.png" alt="enter image description here"></a></p>