[R] How to shade vertical bands in a graph?

[del pes]

Hello,

I would like to draw vertical yellow bands in my graph, but could not find how to do that in the documentation.

I set up a page to show what I would like to achieve: http://rstudent.blogg.de/eintrag.php?id=1 (the first picture was manually colored with the Gimp).

Any help would be welcome...

All the best,

Delfina
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