dichroma — color vision simulator & audit

Scientifically accurate color-vision-deficiency simulator and contrast checker

See your site the way color-blind users see it — and catch the contrast failures only they experience. dichroma applies scientifically accurate color-vision-deficiency (CVD) simulation to any page, live. Pick a deficiency type, drag the severity slider, and the page re-renders the way a person with protanopia, deuteranopia, tritanopia, or complete color blindness perceives it. Then run the built-in contrast audit: it re-checks the page's text in the SIMULATED color space and surfaces text that passes WCAG for typical vision but becomes hard to read under color blindness — failures ordinary contrast checkers cannot report. WHY DICHROMA • Scientifically accurate: implements the peer-reviewed Viénot (1999), Brettel (1997), and Machado (2009) models with correct linear-RGB math, validated against the DaltonLens reference data — not a rough approximation. • Adjustable severity: simulate anything from mild anomalous trichromacy to complete dichromacy with a 0–100% slider. Chrome DevTools' built-in emulation only offers fixed, full-severity rendering. • A contrast audit no other checker does: WCAG ratios are re-computed after mapping both text and background colors through the CVD model, finding red/green pairs that read fine for most people but fail for roughly 1 in 12 men. FEATURES • Five simulation modes: Protanopia, Deuteranopia, Tritanopia, Achromatopsia, or off — anomaly variants via the severity slider • Severity slider (0–100%) with live re-rendering • Optional "Keep across page navigation": re-applies your simulation after reloads and navigation (asks for host access only if you opt in) • Assignable keyboard shortcut to toggle the simulation (chrome://extensions/shortcuts) • Side-panel contrast audit with grouped results: "readable now but fails under CVD", "already failing WCAG for everyone", and "needs review" • Original-vs-simulated preview chips on every finding, plus per-type summary counts • Click a finding to scroll to the element, flash it, and show an in-page preview card; flagged elements are outlined by a page overlay • English and Korean UI HONEST LIMITATIONS Top-layer content (open <dialog> elements, fullscreen video) escapes page-level CSS filters and renders unsimulated. chrome:// pages, the Chrome Web Store, and other restricted pages cannot be filtered or audited. The contrast audit inspects the top-level frame only — iframe content is skipped. Simulated ratios are estimates derived from CVD color models, not a normative WCAG verdict; treat findings as candidates for human review. PRIVACY dichroma collects no data of any kind. All color analysis runs locally in your browser; the extension makes no network requests. The only stored data are your own settings and per-tab audit results, kept in Chrome's extension storage on your machine. THIRD-PARTY SOFTWARE The contrast audit ships axe-core (© Deque Systems, Inc., MPL-2.0) unmodified as vendor/axe.min.js, with its license included in the package at vendor/LICENSE. Source code: https://github.com/yeonjin1357/dichroma