title: How to add multiple geom_hlines with color equal to grouping variable
body: <p>I've created a grouped boxplot and added three specific <code>geom_hlines</code> to the plot. However, I want to set the hline colors to <code>fill=factor(Training.Location)</code>, rather than trying to match the colors manually with a color palette. Is there a way to do this?</p>
  
  <pre><code>ggplot(aes(x=factor(CumDes),y=Mn_Handle), data=NH_C) +
      geom_boxplot( aes(fill=factor(Training.Location))) +
      geom_point( aes(color=factor(Training.Location)), 
      position=position_dodge(width=0.75) ) + 
      theme(axis.ticks = element_blank(), axis.text.x = element_blank()) + 
      coord_cartesian(ylim = c(0, 2000)) + 
      geom_hline(yintercept=432, linetype="dashed", lwd=1.2) + 
      geom_hline(yintercept=583, linetype="dashed", lwd=1.2) + 
      geom_hline(yintercept=439, linetype="dashed", lwd=1.2)
  </code></pre>