title: Changing color of data points in ggplot
body: <p>First I run this code and it works perfectly (all data points turn blue):</p>
  
  <pre><code>ggplot(data = mpg) + geom_point(mapping = aes(x = displ, y = hwy), color = "blue")
  </code></pre>
  
  <p>But when I try move around the mapping like below, the data points turn black instead of blue. </p>
  
  <p>Why is that?</p>
  
  <pre><code>ggplot(data = mpg, mapping = aes(x = displ, y = hwy), color = "blue") + geom_point() 
  </code></pre>