title: How can I use different background color each x value in ggplot?
body: <p>I want to create a boxplot using ggplot library in R.
  What I want is that set various background color to each x value such as a following image. I cannot find any option for changing bgcolor of each x axis. Only thing I found is for changing entire background color such as 'theme_bw()' option</p>
  <p><img src="https://i.stack.imgur.com/AXA75.png" alt="my goal" /></p>
  <p>On first, fourth, fifth x axis, bgcolor is blue. However, there is no value on second, third, sixth x axis, so I want to set red color as bgcolor.</p>
  <p>Thanks for your time!</p>