In ggplot2, how can I change the border of selected facets?

Question

Taking the graph from ggplot2 help pages:

ggplot(mtcars, aes(factor(cyl))) + geom_bar() + facet_grid(. ~ vs)

Is it possible to change the borde

Answer 1

How about filling it with a colour like this?

dd <- data.frame(vs = c(0,1), ff = factor(0:1))
ggplot() + geom_rect(data=dd, aes(fill=ff), 
    xmin=-Inf, xmax=Inf, ymin=-Inf, ymax=Inf, alpha=0.15) + 
    geom_bar(data = mtcars, aes(factor(cyl))) + facet_grid(. ~ vs) + 
    scale_fill_manual(values=c(NA, "red"), breaks=NULL)