title: How to customize lines in ggpairs [GGally]
body: <p>I have the following plot:</p>
  
  <p><img src="https://i.stack.imgur.com/Qkspd.jpg" alt="enter image description here"></p>
  
  <p>Generated with this code:</p>
  
  <pre><code>library("GGally")
  data(iris)
  ggpairs(iris[, 1:4], lower=list(continuous="smooth", params=c(colour="blue")),
    diag=list(continuous="bar", params=c(colour="blue")), 
    upper=list(params=list(corSize=6)), axisLabels='show')
  </code></pre>
  
  <p>My questions are: </p>
  
  <ol>
  <li>How can I change the correlation line to be <code>red</code>, now it's black.</li>
  <li>And the correlation line is buried under the scatter plot. I want to put it on top. How can I do that?</li>
  </ol>