title: Highlight (shade) plot background in specific time range
body: <p>On a generic plot, with time on the x-axis, I would like to highlight a period of some specific years.</p>
  
  <p>How can I bestly do this? My idea is for example a light yellow bar for the highlighted years, behind the plot of course.</p>
  
  <p>The plot code I have now:</p>
  
  <pre><code>pdf("temperature_imfs_big_interm5.pdf", width=6, height=8);
  par(mfrow=c(temperature$bigEmdIm5$nimf+1,1), mar=c(2,1,2,1))
  for(i in 1:temperature$bigEmdIm5$nimf) {
      plot(timeline$big, temperature$bigEmdIm5$imf[,i], type="l", xlab="", ylab="", ylim=range(temperature$bigEmdIm5$imf[,i]), axes=FALSE, main=paste(i, "-th IMF", sep=""))#; abline(h=0)
    axis.POSIXct(side=1, at=tickpos$big)
  }
  plot(timeline$big, temperature$bigEmdIm5$residue, xlab="", ylab="", axes=FALSE, main="residue", type="l")
  axis.POSIXct(side=1, at=tickpos$big)
  dev.off();
  </code></pre>
  
  <p>Where temperature$bigEmdIm5 is the output of emperical mode decompostion. The data is in months, so I would like to higlight 01/1950 until 12/1950 for example.</p>