title: Color points by their occurrence count in ggplot2 geom_count
body: <p>I want to color the points drawn by ggplot2's <code>geom_count</code> based on their count.</p>
  
  <p>This is what I have so far:</p>
  
  <pre><code>ggplot(test3, aes(eleStart, eleLength)) +  geom_count(aes(alpha=0.25, color= ..prop..)) +
    scale_y_continuous(breaks=seq(0,130,5)) +
    scale_x_continuous(breaks=seq(0,114)) +
    theme(panel.grid.minor = element_blank())
  </code></pre>
  
  <p>Now I basically just want to exchange the <code>color=..prop..</code> with the actual count calculated by <code>geom_count</code>, not their proportion.</p>
  
  <p>test3 dataframe looks like:</p>
  
  <pre><code># A tibble: 294 x 2
  # Groups:   X1 [56]
  eleStart eleLength
  &lt;int&gt;     &lt;int&gt;
  1        0         3
  2        0         6
  3        0         7
  4        0         9
  5        0        11
  6        0        23
  7        0        25
  8        0        26
  9        0        26
  10       0        26
  # ... with 284 more rows
  </code></pre>