Contrast pairs Every CSS named color, as text on every other

• The colors. The 148 named colors of CSS Color Module Level 4, from aliceblue to yellowgreen. 139 distinct values: gray and grey, aqua and cyan, fuchsia and magenta are among the names that share one.
• WCAG 2. Relative luminance from the sRGB values, then (L1 + 0.05) / (L2 + 0.05) with the lighter color on top. The linearization switches at 0.04045; WCAG 2’s text says 0.03928, and for 8-bit values the two give identical results.
• Verdicts. Each verdict compares the unrounded ratio with 4.5, 3 and 7. Rounding the ratio to four decimals changes no verdict in this dataset.
• APCA. APCA-W3 0.0.98G-4g, measured with the first color as text. Here Lc reaches ±107.88; its sign gives the polarity, and pairs too close to measure are 0.
• CIEDE2000. The 2000 color-difference formula on CIELAB computed from sRGB with the D65 white, without chromatic adaptation.
• The code. The site’s color engine, the code its contrast tools run, wrote the files. reproduce.mjs, published with them, carries the same formulas and rebuilds contrast-pairs.csv from colors.csv byte for byte, with Node.js alone.

• Names and values. All 148 of the 148 named colors match the table in CSS Color Module Level 4 (9 October 2026).
• WCAG 2. Every luminance and every unrounded ratio is identical to culori 4.0.2; the published ratios differ by at most 0.00005, the rounding.
• APCA. Every Lc matches apca-w3 0.1.9, the reference implementation, within 0.005, the rounding.
• CIEDE2000. Every value matches the delta-e package 0.0.8 within 0.005, the rounding. On culori’s own CIELAB, whose D65 white differs in the fourth decimal, the values move by at most 0.015.
• Structure. 21,904 rows, one for each ordered pair of names; ratios and ΔE are the same both ways; a positive Lc always has the darker color as text, and a negative one the lighter.
• Rebuild. reproduce.mjs, run on colors.csv, writes a contrast-pairs.csv with the published SHA-256.
• The examples. The Python and JavaScript programs below were run on the CSV (Python 3.12.12, Node.js v24.11.0) and printed exactly the output shown.

import csv

with open("contrast-pairs.csv", newline="", encoding="utf-8") as f:
    rows = list(csv.DictReader(f))

aa = [r for r in rows if r["wcag_aa"] == "true"]
print(len(rows), "pairs;", len(aa), "pass AA for body text")

# Which backgrounds take the most named colors as body text?
counts = {}
for r in aa:
    counts[r["background_name"]] = counts.get(r["background_name"], 0) + 1
for name, n in sorted(counts.items(), key=lambda kv: (-kv[1], kv[0]))[:3]:
    print(name, n)

# Pairs WCAG 2 passes that APCA measures below Lc 60.
low = [r for r in aa if abs(float(r["apca_lc"])) < 60]
print(len(low), "pass AA but measure below Lc 60")

import { readFileSync } from "node:fs";

const [head, ...lines] = readFileSync("contrast-pairs.csv", "utf8").trim().split(/\r?\n/);
const keys = head.split(",");
const rows = lines.map((line) => Object.fromEntries(line.split(",").map((v, i) => [keys[i], v])));

const aa = rows.filter((r) => r.wcag_aa === "true");
console.log(rows.length, "pairs;", aa.length, "pass AA for body text");

// Which backgrounds take the most named colors as body text?
const counts = new Map();
for (const r of aa) counts.set(r.background_name, (counts.get(r.background_name) || 0) + 1);
[...counts]
  .sort((a, b) => b[1] - a[1] || a[0].localeCompare(b[0]))
  .slice(0, 3)
  .forEach(([name, n]) => console.log(name, n));

// Pairs WCAG 2 passes that APCA measures below Lc 60.
const low = aa.filter((r) => Math.abs(Number(r.apca_lc)) < 60);
console.log(low.length, "pass AA but measure below Lc 60");

21904 pairs; 3484 pass AA for body text
black 116
navy 97
darkblue 96
650 pass AA but measure below Lc 60

Rebuild the CSV

In a folder with colors.csv, reproduce.mjs and SHA256SUMS.txt, this writes contrast-pairs.csv and checks it against the published checksum.

node reproduce.mjs
sha256sum --ignore-missing -c SHA256SUMS.txt

Auric Artisan. (2026). CSS named color contrast pairs (Version 1.0.0) [Data set]. https://auricartisan.com/datasets/contrast-pairs/1.0.0/

@misc{auricartisan_contrast_pairs_1_0_0,
  author       = {{Auric Artisan}},
  title        = {{CSS} named color contrast pairs},
  year         = {2026},
  version      = {1.0.0},
  howpublished = {\url{https://auricartisan.com/datasets/contrast-pairs/1.0.0/}},
  note         = {Data set. Licensed {CC BY 4.0}}
}

License: Creative Commons Attribution 4.0 International. The color names and values come from CSS Color Module Level 4, a W3C specification.

1. 1.0.011 October 2026First release: 21,904 pairs of 148 named colors.

• WCAG 2 against APCA on 16.8 million pairs
• WCAG 2 and APCA, explained
• Check a pair with both methods
• Check any pair in the contrast checker