DevTut

# Color schemes for graphics

# A handy function to glimse a vector of colors

Quite often there is a need to glimpse the chosen color palette. One elegant solution is the following self defined function:

color_glimpse <- function(colors_string){
        n <- length(colors_string)
        hist(1:n,breaks=0:n,col=colors_string)
}

An example of use

color_glimpse(blues9)

pal (opens new window)

# colorspace - click&drag interface for colors

The package colorspace provides GUI for selecting a palette. On the call of choose_palette() function the following window pops-up:

enter image description here (opens new window)

When the palette is chosen, just hit OK and do not forget to store the output in a variable, e.g. pal.

pal <- choose_palette()

The output is a function that takes n (number) as input and produces a color vector of length n according to the selected palette.

pal(10)
[1] "#023FA5" "#6371AF" "#959CC3" "#BEC1D4" "#DBDCE0" "#E0DBDC" "#D6BCC0" "#C6909A" "#AE5A6D" "#8E063B"

# Colorblind-friendly palettes

Even though colorblind people can recognize a wide range of colors, it might be hard to differentiate between certain colors.

RColorBrewer provides colorblind-friendly palettes:

library(RColorBrewer)
display.brewer.all(colorblindFriendly = T)

colorblind-friendly palette (opens new window)

The Color Universal Design (opens new window) from the University of Tokyo proposes the following palettes:

#palette using grey
cbPalette <- c("#999999", "#E69F00", "#56B4E9", "#009E73", "#F0E442", "#0072B2", "#D55E00", "#CC79A7")

#palette using black
cbbPalette <- c("#000000", "#E69F00", "#56B4E9", "#009E73", "#F0E442", "#0072B2", "#D55E00", "#CC79A7")

# viridis - print and colorblind friendly palettes

Viridis (named after the chromis viridis fish (opens new window)) is a recently developed color scheme for the Python library matplotlib (opens new window) (the video presentation by the link explains how the color scheme was developed and what are its main advantages). It is seamlessly ported to R.

There are 4 variants of color schemes: magma, plasma, inferno, and viridis (default). They are chosen with the option parameter and are coded as A, B, C, and D, correspondingly. To have an impression of the 4 color schemes, look at the maps:

enter image description here (opens new window) (image souce (opens new window))

The package can be installed from CRAN (opens new window) or github (opens new window).

The vignette (opens new window) for viridis package is just brilliant.

Nice feature of the viridis color scheme is integration with ggplot2. Within the package two ggplot2-specific functions are defined: scale_color_viridis() and scale_fill_viridis(). See the example below:

library(viridis)
library(ggplot2)

gg1 <- ggplot(mtcars)+
    geom_point(aes(x = mpg, y = hp, color = disp), size = 3)+
    scale_color_viridis(option = "B")+
    theme_minimal()+
    theme(legend.position = c(.8,.8))

gg2 <- ggplot(mtcars)+
        geom_violin(aes(x = factor(cyl), y = hp, fill = factor(cyl)))+
        scale_fill_viridis(discrete = T)+
        theme_minimal()+
        theme(legend.position = 'none')

library(cowplot)
output <- plot_grid(gg1,gg2, labels = c('B','D'),label_size = 20)
print(output)

enter image description here (opens new window)

# RColorBrewer

ColorBrewer (opens new window) project is a very popular tool to select harmoniously matching color palettes. RColorBrewer is a port of the project for R and provides also colorblind-friendly palettes.

An example of use

colors_vec <- brewer.pal(5, name = 'BrBG')
print(colors_vec)
[1] "#A6611A" "#DFC27D" "#F5F5F5" "#80CDC1" "#018571"

RColorBrewer creates coloring options for ggplot2: scale_color_brewer and scale_fill_brewer.

library(ggplot2)
ggplot(mtcars)+
        geom_point(aes(x = mpg, y = hp, color = factor(cyl)), size = 3)+
        scale_color_brewer(palette = 'Greens')+
        theme_minimal()+
        theme(legend.position = c(.8,.8))

enter image description here (opens new window)

# basic R color functions

Function colors() lists all the color names that are recognized by R. There is a nice PDF (opens new window) where one can actually see those colors.

colorRampPalette creates a function that interpolate a set of given colors to create new color palettes. This output function takes n (number) as input and produces a color vector of length n interpolating the initial colors.

pal <- colorRampPalette(c('white','red'))
pal(5)
[1] "#FFFFFF" "#FFBFBF" "#FF7F7F" "#FF3F3F" "#FF0000"

Any specific color may be produced with an rgb() function:

rgb(0,1,0)

produces green color.

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