title: Setting a common year color between multiple ggplots?
body: <p>I have a cleaned dataset (DropBox: [[[removed - comment if you need an updated copy for working example]]]) of expenditures between 2001 and 2014.  I have three plots - a boxplot, and two scatters - that I am <code>grid.arrange</code>ing into a column for comparison.  For this reason, I'd like the years to be aligned top-to-bottom, and for each year to have a single color common between the graphs - again, for comparison.  </p>
  
  <p>Here is my product, so far (everything's working on this end, just unsure how to align the mappings)</p>
  
  <pre><code>require(ggplot2)
  require(gridExtra)
  require(ggthemes)
  require(lubridate)
  
  options(scipen=999)
  
  date &lt;- exp.s$Date
  amount &lt;- exp.s$Amount
  N &lt;- exp.s$total
  xy &lt;- data.frame(date, amount, N)
  
  #boxplot, color by year of payment
  b1&lt;-ggplot(xy, aes(x = as.factor(year(date)), amount)) + 
   geom_boxplot(aes(fill = as.factor(exp.s$start_year))) +
   scale_color_gdocs() + 
   theme_gdocs()
  
  #jitter plot, color by year of payment
  b2&lt;-ggplot(xy, aes(x = as.factor(year(date)), amount))  + 
   geom_jitter(alpha=I(.8), aes(color=as.factor(year(date)), size = exp.s$tot)) + 
   scale_color_gdocs() + theme_gdocs()
  
  #jitter, color by contract start year
  b3&lt;-ggplot(xy, aes(x = as.factor(year(date)), amount))  + 
   geom_jitter(alpha=I(.9), aes(color=as.factor(exp.s$start_year), size = exp.s$tot)) + 
   scale_color_gdocs() + theme_gdocs()
  
  
  grid.arrange(b1, b2, b3, ncol=1)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/A0t6B.jpg" alt="enter image description here"></p>