ggplot and the invisible hex code.

If you use an eight digit hex code for specifying a color value, the first two control transparency. Thus, you can set fill = “#00000000” in ggplot to get a boxplot with no fill. Here’s a (somewhat contrived) use case: points on top occlude the cross bar but box on top hides the observations.

library(ggplot2)
data.frame(y = 0, x = 1:9) |>
  ggplot(aes(x = x, y = y))+
  geom_point(color = 'firebrick')+
  geom_boxplot(fill = '#00000000')