All right, let\'s say I have the following plot.
df = data.frame(date=c(rep(2008:2013, by=1)),
value=c(303,407,538,696,881,1094))
barplot(df
One Google search later we've learned that you can set the entire plotting device background color as Owen indicates. If you just want the plotting region altered, you have to do something like what is outlined in that R-Help thread:
plot(df)
rect(par("usr")[1],par("usr")[3],par("usr")[2],par("usr")[4],col = "gray")
points(df)
The barplot function has an add parameter that you'll likely need to use.