library(khroma)
1. Introduction
Tol (2021) offers carefully chosen schemes, ready for each type of data, with colors that are:
- Distinct for all people, including color-blind readers,
- Distinct from black and white,
- Distinct on screen and paper,
- Matching well together.
All the scales presented in Paul Tol’s technical note (issue 3.2, 2021-08-18) are implemented here, for use with base R graphics, ggplot2 or ggraph.
2. Qualitative data
According to Paul Tol’s technical note, the bright, contrast, vibrant and muted color schemes are color-blind safe.
The light color scheme is reasonably distinct for both normal or color-blind vision and is intended to fill labelled cells.
The pale and dark schemes are not very distinct in either normal or color-blind vision and should be used as a text background or to highlight a cell in a table.
The qualitative color schemes must be used as given (no interpolation): colors are picked up to the maximum number of supported values. Refer to the original document for details about the recommended uses (see references).
| Scheme | Max. colors |
|---|---|
bright |
7 |
high contrast |
3 |
vibrant |
7 |
muted |
9 |
medium contrast |
3 |
pale |
6 |
dark |
6 |
light |
9 |
2.1 bright
bright <- color("bright")
plot_scheme(bright(7), colours = TRUE, names = TRUE, size = 0.9)
plot of chunk tol_quali_bright
2.2 high contrast
highcontrast <- color("high contrast")
plot_scheme(highcontrast(3), colours = TRUE, names = TRUE, size = 0.9)
plot of chunk tol_quali_highcontrast
2.3 vibrant
vibrant <- color("vibrant")
plot_scheme(vibrant(7), colours = TRUE, names = TRUE, size = 0.9)
plot of chunk tol_quali_vibrant
2.4 muted
muted <- color("muted")
plot_scheme(muted(9), colours = TRUE, names = TRUE, size = 0.9)
plot of chunk tol_quali_muted
2.5 medium contrast
mediumcontrast <- color("medium contrast")
plot_scheme(mediumcontrast(6), colours = TRUE, names = TRUE, size = 0.9)
plot of chunk tol_quali_mediumcontrast
2.6 pale and dark
pale <- color("pale")
plot_scheme(pale(6), colours = TRUE, names = TRUE, size = 0.9)
plot of chunk tol_quali_pale_dark
dark <- color("dark")
plot_scheme(dark(6), colours = TRUE, names = TRUE, size = 0.9)
plot of chunk tol_quali_pale_dark
2.7 light
light <- color("light")
plot_scheme(light(9), colours = TRUE, names = TRUE, size = 0.9)
plot of chunk tol_quali_light
3. Diverging data
If more colors than defined are needed from a given scheme, the color coordinates are linearly interpolated to provide a continuous version of the scheme.
| Scheme | Num. of colors | Bad data |
|---|---|---|
sunset |
11 | #FFFFFF |
nightfall |
17 | #FFFFFF |
BuRd |
9 | #FFEE99 |
PRGn |
9 | #FFEE99 |
3.1 sunset
sunset <- color("sunset")
plot_scheme(sunset(11), colours = TRUE, size = 0.9)
plot of chunk tol_div_sunset
3.2 nightfall
nightfall <- color("nightfall")
plot_scheme(nightfall(17), colours = TRUE, size = 0.9)
plot of chunk tol_div_nightfall
3.3 BuRd
BuRd <- color("BuRd")
plot_scheme(BuRd(9), colours = TRUE, size = 0.9)
plot of chunk tol_div_BuRd
3.4 PRGn
PRGn <- color("PRGn")
plot_scheme(PRGn(9), colours = TRUE, size = 0.9)
plot of chunk tol_div_PRGn
4. Sequential data
If more colors than defined are needed from a given scheme, the color coordinates are linearly interpolated to provide a continuous version of the scheme, with the exception of the discrete rainbow scheme (see below).
| Scheme | Num. of colors | Bad data |
|---|---|---|
YlOrBr |
9 | #888888 |
iridescent |
23 | #999999 |
incandescent |
11 | #888888 |
discrete rainbow |
23 | #777777 |
smooth rainbow |
34 | #666666 |
4.1 YlOrBr
YlOrBr <- color("YlOrBr")
plot_scheme(YlOrBr(9), colours = TRUE, size = 0.9)
plot of chunk tol_seq_YlOrBr
4.2 iridescent
iridescent <- color("iridescent")
plot_scheme(iridescent(23), colours = TRUE, size = 0.5)
plot of chunk tol_seq_iridescent
4.3 incandescent
incandescent <- color("incandescent")
plot_scheme(incandescent(11), colours = TRUE, size = 0.5)
plot of chunk tol_seq_incandescent
4.4 rainbow
As a general rule, ordered data should not be represented using a rainbow scheme. There are three main arguments against such use (Tol 2021):
- The spectral order of visible light carries no inherent magnitude message.
- Some bands of almost constant hue with sharp transitions between them, can be perceived as jumps in the data.
- Color-blind people have difficulty distinguishing some colors of the rainbow.
If such use cannot be avoided, Paul Tol’s technical note provides two color schemes that are reasonably clear in color-blind vision. To remain color-blind safe, these two schemes must comply with the following conditions:
discrete rainbow : This scheme must not be interpolated.
smooth rainbow : This scheme does not have to be used over the full range. Tol (2021) suggests starting at purple.
discrete_rainbow <- color("discrete rainbow")
plot_scheme(discrete_rainbow(14), colours = TRUE, size = 0.7)
plot of chunk tol_seq_rainbow
When using the smooth rainbow scheme:
- Start off-white instead of purple if the lowest data value occurs often;
- End at red instead of brown the highest data value occurs often.
smooth_rainbow <- color("smooth rainbow")
## Start at purple instead of off-white
plot(smooth_rainbow(256, range = c(0.25, 1)))
plot of chunk tol_seq_adjust
## End at red instead of brown
plot(smooth_rainbow(256, range = c(0, 0.9)))
plot of chunk tol_seq_adjust
5. Diagnostic maps
5.1 Qualitative color schemes
Diagnostic maps for the bright, vibrant, muted and light (from top to bottom) qualitative color schemes.
5.2 Diverging schemes
Diagnostic maps for the sunset, BuRd and PRGn (from top to bottom) diverging color schemes.
Diagnostic maps for the sunset, BuRd and PRGn diverging color schemes.
5.3 Sequential schemes
Diagnostic maps for the YlOrBr, iridescent, discrete rainbow and smooth rainbow (from top to bottom) sequential color schemes.
Diagnostic maps for the YlOrBr, iridescent and smooth rainbow sequential color schemes.
6. References
Tol, P. 2021. “Colour Schemes.” Technical note SRON/EPS/TN/09-002 3.2. SRON. URL: https://personal.sron.nl/~pault/data/colourschemes.pdf.