How to remove gray borders around individual entries in ggplot2 legend when using theme_bw?

Question

I have the following code in R:

library(ggplot2) theme_set(theme_bw()) p <- ggplot(mtcars, aes(wt, mpg)) p <- p + geom_point(aes(colour = factor(cyl))) p 

As a result:

Each legend entry has a gray frame around it. How to remove it?

Answer 1

Just add

 + theme(legend.key = element_rect(colour = NA))