geom_tile legend does not show boundary colour

[kobiperl]

library(ggplot2)
df <- data.frame(x = c(1,2,1,2), y = c(1,1,2,2), type = c('foo','blah','foo','blah'))
ggplot(df, aes(x=x, y=y)) + geom_tile(aes(color = type))

Produces the following image:
Rplot.pdf

Where the guide does not indicate the color.