title: How to Add White Border to colored Geom_Point
body: <p>I am reading <a href="https://r4ds.had.co.nz/data-visualisation.html" rel="nofollow noreferrer">https://r4ds.had.co.nz/data-visualisation.html</a>. Exercise 3.6.1. asks to create this</p>
  
  <p><a href="https://i.stack.imgur.com/lPHKz.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lPHKz.jpg" alt="enter image description here"></a></p>
  
  <p>I tried <code>fill = drv</code></p>
  
  <pre><code>library(tidyverse)
  ggplot(mpg, aes(x = displ, y = hwy)) +
    geom_point(shape = 21, colour = "white", fill = drv, size = 5, stroke = 5)
  </code></pre>
  
  <p>and <code>fill = factor(drv)</code></p>
  
  <pre><code>ggplot(mpg, aes(x = displ, y = hwy)) +
    geom_point(shape = 21, colour = "white", fill = factor(drv), size = 5, stroke = 5)
  </code></pre>
  
  <p>And get error</p>
  
  <blockquote>
    <p>object 'drv' not found</p>
  </blockquote>