Contrasting text colour for labels drawn over a fill colour

Given one or more fill/background colours, returns "white" or "black", whichever gives better contrast against that background. Useful for value labels drawn inside bars or over points/lines, matching the Ipea editorial guidelines for graphics, which alternate the colour of data labels according to how dark the colour behind them is. See https://www.ipea.gov.br/manualeditorial/padroes/padroes-grafico-visuais/ilustracoes-pi.html.

Usage

ipea_contrast_color(background)

Arguments

background

A character vector of colours (hex codes or R colour names) used as the fill/background behind the label.

Value

A character vector the same length as background, containing "white" or "black".

See also

Other ggplot2 theme functions: ipea_label_size(), scale_color_ipea(), scale_fill_ipea(), theme_ipea()

Examples

ipea_contrast_color(c("#29112F", "#D2A0C9"))
#> [1] "white" "black"

library(ggplot2)
df <- data.frame(grupo = c("A", "B"), valor = c(22.6, 4.7),
                  cor = c("#29112F", "#D2A0C9"))
ggplot(df, aes(grupo, valor, fill = cor, label = valor)) +
  geom_col() +
  geom_text(aes(color = ipea_contrast_color(cor)), size = ipea_label_size(),
            fontface = "bold") +
  scale_fill_identity() +
  scale_color_identity() +
  theme_ipea()