title: Making fill colors match in ggplot
body: <p>I am making multiple bar charts. I am using fill to color code based on the levels of a factor. The factor name is Percentile.Category and the levels are 0-25, 26-50, 51-75, 76-90, 91-100. The problem is that not all of the charts have all 5 levels of the factor, so when I use a color palette, the factors don't have the same colors in different charts.</p>
  
  <p>This is an example of the code I have to generate a plot. I basically replicated the same thing with different data frames to produce multiple plots:</p>
  
  <pre><code>UC %&gt;% 
    ggplot(aes(x = reorder(Provider.Name, Score), y = Score)) +
    geom_bar(stat = "identity", aes(fill = Percentile.category)) +
    coord_flip() +
    ggtitle("Urgent Care Percentiles for 'Would Recommend Facility'") +
    ylab("Would You Recommend Top Box") +
    xlab("Provider") +
    scale_fill_brewer(palette = "Spectral") +
    geom_text(aes(label = Score), size = 2.5, vjust = .4, hjust = 1.2, fontface = "bold")
  </code></pre>
  
  <p>Right now, if a particular data frame is missing any data at one of the factor levels, the colors for each factor level change. What I want is for the factor level colors to match in the different plots. For example, 51-75 is the same color in all of them.</p>