How to change the points such that it is filled with color on the inside (according to the factor) but has a white border on the outside? I can't find an example with the standard pch
chart
library(data.table)
A = data.table(x = 1:4, y = 1:4, z = c('A','A','B','B'))
ggplot(A) + geom_point(aes(x = x, y = y, color = z)) + facet_grid(~z) + theme_bw()