r - Overlay grid rather than draw on top of it

Question

I have a ggplot2 graph which appears as follows:

Notice that the grid or axis lines do not show through the ribbons. One way of dealing with this is to alter the alpha property of the ribbons; however, this can make the lighter colours too light.

An alternative idea would be to draw the grid/axis lines on top of the ribbons rather than beneath them. How can I achieve this render ordering?

Naturally, the question could be asked of any plot generated by ggplot2. But a copy-and-paste command that illustrates the issue is as follows:

 ggplot(data.frame(x=sample(1:100),y=sample(1:100)),aes(x=x,y=y))+geom_point(size=20)

Answer 1

ggplot introduced an option in theme() that lets you do just that with pull number 993, on June 18, 2015.

Just add to your plot:

+ theme(
  panel.background = element_rect(fill = NA),
  panel.ontop = TRUE
)

There is an example in the ggplot docs.