density plots without outlines in ggplot2

It is not:

anything in the aes of the ggplot call
color=FALSE
color=NULL

It is:

color=NA in the geom_density call

e.g.

ggplot(data, aes(x=value, fill=grouping))+geom_density(<b>color=NA</b>)

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")