Check that a palette stays distinguishable under each deficiency

For normal vision and each deficiency at full severity, the palette's colours are converted to CIE Lab* and the smallest pairwise colour difference (CIE76 Delta-E) is found. The lower this minimum, the more likely two categories are to be confused. A palette counts as safe when the minimum across all four conditions is at least threshold.

Usage

palette_safety(colours = NULL, threshold = 5)

Arguments

colours

The palette to test. Defaults to the depictr qualitative palette. Needs at least two colours: a pairwise distance over fewer than two has no value, rather than an infinitely safe one.

threshold

The smallest acceptable Delta-E.

Value

A list with min_delta_e (the worst case across conditions), by_condition (a named numeric vector, one minimum Delta-E for normal vision and for each deficiency), worst_condition and worst_pair (the closest colours and where they were closest), safe and threshold.

Details

The default threshold of 5 is calibrated against the reference colourblind-safe palette: the Okabe-Ito set's tightest pair (reddish purple against grey) sits at Delta-E 7.4 under full deuteranopia, so the cut must lie below that to pass the recommended palette, while still flagging colours that become near-identical under a deficiency. The difference includes lightness, which survives colour-vision deficiency, so two colours that share a hue but differ in lightness are correctly treated as distinguishable. Full severity is the worst case; most colour-vision deficiency is milder.

This looks at a palette in the abstract. To audit a finished figure, which uses only as many colours as it has groups and has text and a background besides, see check_figure().

References

Okabe M, Ito K (2008). “Color Universal Design (CUD): How to make figures and presentations that are friendly to colorblind people.” https://jfly.uni-koeln.de/color/. Accessed 2026-06-14.

Machado GM, Oliveira MM, Fernandes LAF (2009). “A physiologically-based model for simulation of color vision deficiency.” IEEE Transactions on Visualization and Computer Graphics, 15(6), 1291–1298. doi:10.1109/TVCG.2009.113 .

Examples

palette_safety()
#> $min_delta_e
#> [1] 7.4
#> 
#> $by_condition
#> normal protan deutan tritan 
#>  33.43  18.15   7.40  16.18 
#> 
#> $worst_condition
#> [1] "deutan"
#> 
#> $worst_pair
#> [1] "#cc79a7" "#999999"
#> 
#> $safe
#> [1] TRUE
#> 
#> $threshold
#> [1] 5
#> 

# Two colours a hair apart are flagged.
palette_safety(c("#005b96", "#015c97"))
#> $min_delta_e
#> [1] 0.41
#> 
#> $by_condition
#> normal protan deutan tritan 
#>   0.42   0.41   0.42   0.41 
#> 
#> $worst_condition
#> [1] "protan"
#> 
#> $worst_pair
#> [1] "#005b96" "#015c97"
#> 
#> $safe
#> [1] FALSE
#> 
#> $threshold
#> [1] 5
#>