Colour in Data Visualisation

Choosing colour for charts and maps: categorical, sequential and diverging palettes, why rainbow scales mislead, and how to keep a chart readable in greyscale, dark mode and for colour-vision deficiency.

Covers colour decisions in charts and maps, not chart design generally.

11 topics · 41 evidence-labelled claims · 18 sources

Tools

Chart palette checker

Palette types

Categorical, sequential and diverging.

How do you choose colours for categories in a chart?Give each category a hue that differs clearly from every other, keep lightness and chroma similar so no category looks more impor…How should a colour scale show low-to-high values?Map the data to lightness: light for low values and dark for high (or the reverse on a dark background), in steps that look equal.When should a chart use a diverging colour scale?Use a diverging scale only when the data have a meaningful midpoint — zero, an average, a target — and both directions away from…

How colour misleads

Rainbow scales, luminance and emphasis.

Why are rainbow colour scales bad for data?A rainbow (jet or HSV-style) scale runs through hues whose lightness goes up and down rather than in one direction, so it has no…How do you use colour to highlight one thing in a chart?Make everything else quiet — usually grey — and give the one series or bar that matters a single saturated colour that also diffe…Should charts use red for bad and green for good?Only with care.

Robust charts

CVD, greyscale, print and dark mode.

How do you make a chart readable for colour-blind readers?Choose colours that stay apart under simulated protanopia, deuteranopia and tritanopia — usually by making them differ in lightne…Do chart colours need to change for dark mode?Usually, yes.How do you make a colour chart work when printed in black and white?Make sure the colours that must be told apart differ in lightness, not just hue, because greyscale keeps only lightness.How many colour classes should a choropleth map use?Usually five to seven.What colour should missing data be on a chart or map?Something that cannot be mistaken for any value on the scale — usually a pattern or hatch, or a neutral grey clearly outside the…