title: How to add a ggplot2 subtitle with different size and colour?
body: <p>I'm using ggplot2 to improve precipitation barplots.</p>
  
  <p>Here's a reproducible example of what I want to achieve: </p>
  
  <pre><code>library(ggplot2)
  library(gridExtra)
  secu &lt;- seq(1, 16, by=2)
  melt.d &lt;- data.frame(y=secu, x=LETTERS[1:8])
  m &lt;- ggplot(melt.d, aes(x=x, y=y)) +
    geom_bar(fill="darkblue") + 
    labs(x="Weather    stations", y="Accumulated Rainfall [mm]") +
    opts(axis.text.x=theme_text(angle=-45, hjust=0, vjust=1),
         title=expression("Rainfall"), plot.margin = unit(c(1.5, 1, 1, 1), "cm"),
         plot.title = theme_text(size = 25, face = "bold", colour = "black", vjust = 5))
  z &lt;- arrangeGrob(m, sub = textGrob("Location", x = 0, hjust = -3.5, vjust = -33, gp = gpar(fontsize = 18, col = "gray40"))) #Or guessing x and y with just option
  z
  </code></pre>
  
  <p>I don't know how to avoid using guessing numbers on hjust and vjust on ggplot2? Is there a better way to put a subtitle (not just using \n, but a subtitle with different text color and size)?</p>
  
  <p>I need to be able to use with ggsave to have a pdf file.</p>
  
  <p>Here are two related questions:</p>
  
  <p><a href="https://stackoverflow.com/questions/10197738/add-a-footnote-citation-outside-of-plot-area-in-r">Add a footnote citation outside of plot area in R?</a></p>
  
  <p><a href="https://stackoverflow.com/questions/3864535/how-can-i-add-a-subtitle-and-change-the-font-size-of-ggplot-plots-in-r">How can I add a subtitle and change the font size of ggplot plots in R?</a></p>
  
  <p>Thanks for any help.</p>