[R] ggplot2: Changing colour scheme for bar plot filling?

[Johannes Graumann]

Hello,

I'd like to sitch to a monochrome/bw color-palette for the filling of 
geom_bar-bars (produced via "qplot" as in the example below). Hours of 
googling didn't yield anything useful, so I thought, I'd just ask ...

Thanks, Joh

library(ggplot2)
qplot(factor(cyl), data=mtcars, geom="bar", fill=factor(cyl))