dichroma — color vision simulator & audit

About

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