title: Only display specific labels of a ggplot legend
body: <p>I have some data points, and I want to single out some of the points in my visualization. I would do it like this:</p>
  
  <pre><code>df = data.frame(
    x = 1:4, y = 1:4,
    special = c('normal', 'normal', 'normal', 'special')
  )
  
  ggplot(df) +
    geom_point(aes(x, y, color = special)) +
    scale_color_manual(values = c('red', 'black')) +
    labs(color = "") +
    theme_bw()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/qdnBV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qdnBV.png" alt="example"></a></p>
  
  <p>My issue here is that the black points are very self explanatory and don't need a label. I want <em>just</em> the red "special" label to appear. Is there a way I can hide the "normal" label?</p>