title: Color points in overlayed scatterplots in ggplot R
body: <p>Using this tibble as example:</p>
  
  <pre><code>tibble(
    groups = c("a","b","c","d","e"),
    grade1 = c(510,405,308,201,99),
    grade2 = c(520,430,300,190,110),
    grade3 = c(530,410,320,210,105)
  )
  </code></pre>
  
  <p>How do I manage to color the points according to the grade # using geom_point? I've tried plotting it like this...</p>
  
  <pre><code>ggplot(aes(x=groups)) +
      geom_point(aes(y=grade1))+
      geom_point(aes(y=grade2))+
      geom_point(aes(y=grade3))
  </code></pre>
  
  <p>...and <code>color="red"</code>, or any other color, always leads to the same shade of orange. </p>