title: Add Legend and change Colour on grouped bar plot
body: <p>I created a plot like this;</p>
  
  <pre><code>library("ggplot2")    
  ggplot(data = diamonds) + 
        geom_bar(mapping = aes(x = color, y = ..prop.., group = 2)) + 
        scale_y_continuous(labels=scales::percent) +
        facet_grid(~cut)
  </code></pre>
  
  <p>Now I want to add a legend for the variable "color", also I want to change the colour of the bars. The graph is exactly how I want it to be, and if possible I don't want change the structure of the dataset, just add a legend and change colours.</p>
  
  <p>I could not find example that fit for this "percentage"-style graphics.</p>