density plots without outlines in ggplot2

It is not:

It is:

e.g.

    ggplot(data, aes(x=value, fill=grouping))+geom_density(color=NA)

Example (this is some real data I'm currently working with, but I've changed the labels so it's hopefully not meaningful):

Code:

    ggplot(data, aes(x=variable, fill=switch)) +
    geom_density(alpha=0.7, color=NA) +
    facet_grid(case~condition) +
    xlim(-3,3) + theme_bw() + 
    scale_fill_manual(values=c("darkorchid2","darkturquoise")) +
    ggtitle("density plots with no outline")