Palettes for fourfold displays

fourfold_palette() returns six colors for the palette argument of geom_fourfold(). The colors encode the direction and statistical strength of association and are drawn directly by the geom rather than through a fill scale. Entries 1-2 are used when extended = FALSE (or conf_level = 0), entries 3-4 are used for a stratum whose association is not significant after adjustment, and entries 5-6 are used for a stratum whose association is significant after adjustment. Within each pair, the first color fills the diagonal with fewer cases than expected under independence and the second fills the diagonal with more.

Usage

fourfold_palette(palette = c("vcd", "okabe-ito"))

Arguments

palette: Name of the palette: "vcd" (the default) or "okabe-ito".

Value

A character vector containing six hexadecimal colors.

Details

"vcd", the default, gives the colors of vcd::fourfold() (Meyer et al., 2026): light and darker blue, then light red and light blue, then red and navy.

"okabe-ito" uses the colors of Okabe and Ito (2008), chosen to remain distinguishable for readers with common forms of color-vision deficiency: sky blue and blue, then orange and sky blue lightened about halfway to white, then vermilion and blue.

References

Meyer, D., Zeileis, A., Hornik, K., & Friendly, M. (2026). vcd: Visualizing Categorical Data (R package). doi:10.32614/CRAN.package.vcd

Okabe, M., & Ito, K. (2008). Color Universal Design (CUD): How to make figures and presentations that are friendly to colorblind people. https://jfly.uni-koeln.de/color/

Examples

fourfold_palette()
#> [1] "#99CCFF" "#6699CC" "#FFA0A0" "#A0A0FF" "#FF0000" "#000080"
fourfold_palette("okabe-ito")
#> [1] "#56B4E9" "#0072B2" "#F2CF7F" "#AAD9F3" "#D55E00" "#0072B2"

ucb <- as.data.frame(UCBAdmissions)

ggplot2::ggplot(
  ucb,
  ggplot2::aes(x = Gender, y = Admit, weight = Freq)
) +
  geom_fourfold(palette = fourfold_palette("okabe-ito")) +
  ggplot2::facet_wrap(ggplot2::vars(Dept), ncol = 3) +
  theme_fourfold()