Paul Tol's Color Schemes
Details
The maximum number of supported colors is only relevant for the qualitative color schemes (divergent and sequential schemes are linearly interpolated).
- Qualitative data
bright
(7),high contrast
(3),vibrant
(7),muted
(9),medium contrast
(6),pale
(6),dark
(6),light
(9).- Diverging data
sunset
(11),nightfall
(17),BuRd
(9),PRGn
(9).- Sequential data
YlOrBr
(9),iridescent
(23),incandescent
(11),discrete rainbow
(23),smooth rainbow
(34).
Qualitative Color Schemes
The qualitative color schemes are used as given (no interpolation): colors are picked up to the maximum number of supported values.
Palette | Max. |
bright | 7 |
highcontrast | 3 |
vibrant | 7 |
muted | 9 |
mediumcontrast | 6 |
pale | 6 |
dark | 6 |
light | 9 |
According to Paul Tol's technical note, the bright
, highcontrast
,
vibrant
and muted
color schemes are color-blind safe. The
mediumcontrast
color scheme is designed for situations needing color
pairs.
The light
color scheme is reasonably distinct for both normal or
colorblind vision and is intended to fill labeled cells.
The pale
and dark
schemes are not very distinct in either normal or
colorblind vision and should be used as a text background or to highlight
a cell in a table.
Refer to the original document for details about the recommended uses (see references)
Diverging Color Schemes
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.
Palette | Max. | NA value |
sunset | 11 | #FFFFFF |
nightfall | 17 | #FFFFFF |
BuRd | 9 | #FFEE99 |
PRGn | 9 | #FFEE99 |
Sequential Color Schemes
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.
Palette | Max. | NA value |
YlOrBr | 9 | #888888 |
iridescent | 23 | #999999 |
discreterainbow | 23 | #777777 |
smoothrainbow | 34 | #666666 |
Rainbow Color Scheme
As a general rule, ordered data should not be represented using a rainbow scheme. There are three main arguments against such use (Tol 2018):
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:
discreterainbow
This scheme must not be interpolated.
smoothrainbow
This scheme does not have to be used over the full range.
References
Tol, P. (2021). Colour Schemes. SRON. Technical Note No. SRON/EPS/TN/09-002, issue 3.2. URL: https://personal.sron.nl/~pault/data/colourschemes.pdf