In ggplot2, how can I make the legend have a semi-transparent background. The following code, gives a fully transparent background (and positioning control) plot <- plot + theme(legend.position=c(1,1),legend.justification=c(1,1), legend.direction="vertical", legend.box="horizontal", legend.box.just = c("top"), legend.background = element_rect(fill="transparent")) But how can one control the level
![Controlling the 'alpha' level in a ggplot2 legend](https://cdn-ak-scissors.b.st-hatena.com/image/square/98d6f053a97a87156775f60757c60865d0f2c47d/height=288;version=1;width=512/https%3A%2F%2Fcdn.sstatic.net%2FSites%2Fstackoverflow%2FImg%2Fapple-touch-icon%402.png%3Fv%3D73d79a89bded)