Easy Way To Expand Color Palettes in R

This article describes how to use the colorRampPalette() R function to expand color palettes. We’ll provide practical example with ggplot2.

The color scales defined in the RColorBrewer and in other packages, such as viridis, have a fixed number of colors.

For example you have 8 colors in the Set2 brewer palette. Consequently, if your data contain more than 8 groups, ggplot2 will return a warning like this:

For example, type this R code:

df <- iris[1:18, ]
df$name <- 1:nrow(df)

library(ggplot2)
ggplot(df) + 
  geom_col(aes(name, Sepal.Length, fill = factor(Sepal.Length))) +
  scale_fill_brewer(palette="Set2") +
  theme_minimal() +
  theme(legend.position = "top")

A solution is to use the function colorRampPalette() which can extend any list of colors:

library(RColorBrewer)
# Define the number of colors you want
nb.cols <- 18
mycolors <- colorRampPalette(brewer.pal(8, "Set2"))(nb.cols)
# Create a ggplot with 18 colors 
# Use scale_fill_manual
ggplot(df) + 
  geom_col(aes(name, Sepal.Length, fill = factor(Sepal.Length))) +
  scale_fill_manual(values = mycolors) +
  theme_minimal() +
  theme(legend.position = "top")

In conclusion, this article describes how to expand color palettes in R.