title: Change fill color of dotplot_geom but retain fill color of boxplot
body: <p>I have included reproducible code from the mtcars data set below:</p>
  
  <pre><code>library(ggplot2)    
  
  ggplot(mtcars,aes(as.factor(vs),disp))+ 
    stat_boxplot(geom ='errorbar',position=position_dodge(width=.88),aes(fill=as.factor(am))) + 
    geom_boxplot(position=position_dodge(width=.88),aes(fill=as.factor(am)))+
    geom_dotplot(binaxis='y', stackdir='center',dotsize=0.25,position=position_dodge(width=.88),stackratio=1.1,aes(fill=as.factor(am),color=as.factor(am)))
  </code></pre>
  
  <p>I would like to make the dots from the dotplot grey/black, while having control over the fill colour of the boxplots.
  As you can see, I need the fill colour aesthetic for both the boxplots and dotplots in order to separate the three factors on the x axis by the necessary group. Additionally, the dotplot's color aesthetic maps to the outline of the dots, while the fill aesthetic maps to the inside of the dots, so I need to use both, since I would like one seamless point. 
  Using the scale_fill_manual function changes the colour of both boxplots and dots, but I need to have control over the colour of both separately.</p>
  
  <p>I have found this other question on stackoverflow but I'm struggling to apply it to my case. </p>
  
  <p><a href="https://stackoverflow.com/questions/34893760/how-to-scale-the-size-of-line-and-point-separately-in-ggplot2/35213634#35213634">How to scale the size of line and point separately in ggplot2</a></p>