How do you choose colors that are both accessible to colorblind viewers and analytically meaningful?
About 8 % of men have red-green color deficiency, making the default red-green diverging palette unreliable. Use colorblind-safe palettes such as Okabe-Ito or ColorBrewer, match palette type to data type (sequential for ordered magnitudes, diverging for values around a meaningful midpoint, qualitative for unordered categories), and always add a redundant encoding such as shape, pattern, or label.
How to think about it
Three palette families
- Sequential (e.g., light blue to dark blue): use when the variable has a natural low-to-high order and zero is not a special value — population density, revenue, temperature in summer.
- Diverging (e.g., blue-white-red): use when there is a meaningful midpoint, such as zero or a target, and deviations in both directions matter — profit margin (negative vs. positive), sentiment score.
- Qualitative (e.g., Okabe-Ito, ColorBrewer Set2): use for unordered categories — product lines, regions, species. Each color should be equally visually salient.
Colorblind-safe choices
Red-green is the most common axis of color deficiency (deuteranopia and protanopia). Avoid any palette where the only distinction between groups is red versus green. Reliable alternatives:
- Okabe-Ito (8-color qualitative, designed for colorblindness)
- ColorBrewer palettes (available in matplotlib, ggplot2, Tableau, and Vega)
- Blue-orange diverging (both visible under deuteranopia)
Redundant encoding
Color should never be the sole encoding. Pair it with:
- Shape on scatter plots (circle vs. triangle vs. square)
- Line style on line charts (solid vs. dashed)
- Direct labels or pattern fills on bar charts
- Position when possible (grouped bars rather than stacked color)
This ensures the chart is still readable when printed in black-and-white or viewed by someone with color deficiency.
Contrast and background
Beyond hue, check luminance contrast. The WCAG AA standard requires a contrast ratio of at least 4.5:1 for text and 3:1 for large graphical elements. Tools like Coblis (color blindness simulator) and the Paletton contrast checker help validate designs before publication.