Color Blind Website Checker

How the website checker works

You paste a URL and the server opens the page in a headless browser — a real rendering engine with no visible window. It waits for the page to load, then captures a full-page screenshot of what actually rendered: your fonts, your images, your CSS, the whole thing. That screenshot is then run through color-blindness simulations, so you review your live site rather than a mockup or a hand-picked swatch. The tool currently simulates the four cases that cover the most ground: protanopia, deuteranopia, tritanopia, and achromatopsia.

The reason to test the rendered page instead of a design file is simple. A palette can pass every contrast check in isolation and still fail in context, because meaning on a real page comes from how colors sit next to each other — a red error message beside black body text, a green status dot beside a gray one. The screenshot captures those relationships as your visitors see them.

Switch between the original and each simulation using the tabs above. Anything that becomes hard to tell apart in a simulated view is worth a second look.

What it tends to catch on real sites

About 300 million people worldwide have some form of color blindness — roughly 1 in 12 men and 1 in 200 women, with red-green deficiency being by far the most common. Once you run a live page through the simulations, the same handful of patterns show up again and again. These are the ones to watch for:

• Links that differ from body text by color alone. A blue link inside a gray paragraph can flatten into the same tone, so the reader has no idea the words are clickable.
• Form errors shown only in red. If the only signal that a field is wrong is a red border or red helper text, a protan or deutan user may never see it.
• Required fields marked by color. A red asterisk or a red field label reads the same as everything else to many people.
• Charts and dashboards that lean on a color key. Multi-series line charts, pie slices, and heat maps are the classic failure — categories collapse together and the legend stops helping.
• Disabled versus active states. A button that only looks disabled because it's a slightly grayer shade can be indistinguishable from the live one.
• Sale and price highlighting. A red “was” price next to a black “now” price loses the contrast that made the discount obvious.
• Hover-only cues. Anything that only announces itself with a color change on hover is easy to miss for anyone, and worse when that color shift is subtle.
• Status pills. Green “online” and red “offline” badges are everywhere in dashboards, and they're one of the most common color-only mistakes on the web.

A practical way to work through the results

Fixing an accessibility problem usually isn't about swapping one color for a prettier one. It's about making sure meaning survives when color drops out, and most fixes come down to the same handful of common UI mistakes that affect color blind users. A workflow that holds up:

1. Capture the page you want to audit, starting with the ones that carry the most weight — signup, checkout, pricing, the main dashboard.
2. Step through each simulation and note every place that becomes ambiguous. Be honest here; if you have to squint, a visitor won't bother.
3. Add a non-color cue to each problem spot. Underline your links. Put an icon and a few words next to an error, not just a red outline. Label chart series directly on the line instead of relying on the legend. Add text like “Online” inside the status pill.
4. Re-run the checker and confirm the ambiguity is gone in every simulated view.

A couple of rules of thumb make the fixes durable: keep body-text contrast at 4.5:1 or higher, and 3:1 for icons, borders, and chart marks; and steer clear of red/green or blue/purple as the only difference between two states.

Why it matters — standards and the legal picture

The common benchmark for web accessibility is WCAG 2.1 at Level AA. Two of its rules speak directly to what this tool checks: color can't be the only way you convey information, and text needs enough contrast to be read. Meeting AA is the target most teams and most contracts are written around.

In the United States, web accessibility is widely litigated under the Americans with Disabilities Act, specifically Title III, which covers places of public accommodation. Federal agencies and their vendors have a separate obligation under Section 508 of the Rehabilitation Act. In the European Union, the reference standard is EN 301 549, which folds in the WCAG success criteria. The details differ by jurisdiction, and none of this is legal advice — but the practical direction is the same everywhere: don't make color the only signal.

There's a plainer business case too. Color blindness affects a large enough share of any audience that color-only cues quietly cost you signups, purchases, and repeat visits. An accessible site is easier to use for far more people than the ones you were specifically designing for.

What this tool can and can't tell you

Being clear about the limits keeps you from trusting it too much. A few things worth knowing:

• It captures the page as it renders at load. Content that only appears after you click a tab, open a menu, or scroll into a lazy-loaded section may not be in the shot.
• Some sites block automated browsers, sit behind a login, or throw up a bot check. Those pages either won't load or will return the wrong thing.
• Simulation is an approximation. It models an average version of each condition; real vision varies from person to person, especially for the milder anomalous types.
• Your monitor matters. An uncalibrated, very bright, or very dim screen shifts the colors you're judging.

Treat this as a design and audit aid, not a medical or legal certification. It can't diagnose color blindness in a person, and it can't certify that a site is legally compliant. If you want to check your own vision, take a color blindness test and see an eye-care professional if anything seems off.

Frequently asked questions

Related reading

• How to improve accessibility for color blind users
• Common UI mistakes that affect color blind users
• How to design for color blind users

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