title: Error: Objects of type lm not supported by autoplot
body: <p>I am trying to create a simple function that accepts two arguments:</p>
  <p>A linear model and a string that corresponds to a color, in that order.</p>
  <p>It should create a Residuals vs Fitted and Q-Q plot for this linear model, and color the points according to the string argument like this:</p>
  <blockquote>
  <p>demo_lm &lt;- lm(ExpenditurePerStud ~ State, data = clean_colleges)</p>
  <p>answer7(demo_lm, &quot;#34925E&quot;)</p>
  </blockquote>
  <p>This is what I have tried:</p>
  <pre><code>library(ggplot2)
  
  demo_lm &lt;- lm(ExpenditurePerStud ~ State, data = clean_colleges)
  
  answer7 &lt;- function( my_lm , color_str) 
  {
    autoplot(my_lm, which = 1:2, smooth.colour = color_str,
             data = clean_colleges, colour = color_str) +
      theme_bw()
  }
  </code></pre>
  <p>But it throws the Error: Objects of type lm not supported by autoplot when I call <code>answer7(demo_lm, &quot;#34925E&quot;)</code></p>