Directly label colored series instead of relying on a color key

Label colored series directly on the chart instead of making readers decode them through a color key. For example, place series names next to lines or areas, or label pie slices directly so readers do not have to match colors back and forth with a legend.

A color key forces readers to translate color into identity before reading the data. Direct labels remove that lookup step and keep identity attached to the mark itself.

Mechanism: Direct labels reduce back-and-forth scanning between the chart and the legend, making category identity readable even when colors are hard to distinguish.

Evidence: The article calls color keys a problem for colorblind people, recommends getting rid of them when possible, and specifically recommends direct labels for line, area, and pie charts. (https://www.datawrapper.de/blog/colorblindness-part2">Muth, 2020)

• User Goal: Identify colored series or slices quickly.
• Task: Lookup and comparison of labeled series.
• Data: A small enough set of categories to label directly.
• Chart Setting: Chart types such as line, area, or pie where labels can sit on or near the marks.
• Audience: Readers who may include people with color-vision deficiency.
• Success Criterion: Readers can identify each series without consulting a color key.

Break it when: The chart type cannot place labels directly on the marks. Why: The article gives this recommendation for chart types where direct mark labeling is feasible, such as line, area, and pie charts.

Sacrifice: You give up some empty space near the marks. Risk: Keeping both direct labels and the old color key preserves the same split-attention problem. Mitigation: Remove the color key once the direct labels carry the identity.

Mistake: Leaving colored series unlabeled and expecting the legend to do all identification work. Why it fails: Readers must decode the legend before they can read the chart, and that is especially hard when colors are confusable.

Failure Sign: A reader still has to look at the legend to identify a line, area, or slice. Quick Check: Cover the legend and see whether each marked category is still identifiable. Stronger Test: Run a colorblind simulation and check whether the labels, not just the colors, still carry the identity.

• Place a label directly next to each line or area.
• Label each pie slice directly instead of relying only on a legend.
• Remove the color key once direct labels provide the category names.