IN THIS GUIDE
1. Start with Okabe-Ito
The Okabe-Ito palette (orange, sky blue, bluish green, yellow, blue, vermilion, reddish purple, black) was designed so all eight colours remain distinguishable under the common forms of colour vision deficiency. It is the default safe choice and is built into PaperPict.
2. Never encode with colour alone
Pair colour with a second channel: line style (solid, dashed, dotted), marker shape, fill pattern, or direct labels. If the figure still makes sense in grayscale, it makes sense to everyone.
3. Avoid rainbow and red–green scales
Jet and rainbow colour maps create false boundaries and collapse for red–green deficiency. Use perceptually uniform sequential maps (viridis, cividis) or a two-colour diverging scale with a neutral midpoint.
4. Check contrast against the background
Light yellow on white and dark blue on black both fail. Keep at least a 3:1 contrast ratio between an element and its background, and 4.5:1 for text labels.
5. Simulate before you submit
Run the finished figure through a colour-vision simulator (protanopia, deuteranopia, tritanopia). PaperPict's grayscale check gives a fast first pass; a full simulation is worth doing on the final export.
6. Label directly where you can
Direct labels next to lines and regions remove the need for a legend and the need to match colours at all. This also survives photocopying and low-quality projection.
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