SET IT UP
Colour correction, on whichever surface you actually use. All of it is free and open source, none of it needs an account, and nothing you do here is uploaded anywhere.
FIRST — HOW STRONG?
Correction tuned for complete colour blindness is too strong for most people, and at that setting it distorts far more than it helps. Most colour-vision deficiency is partial. So the strength matters as much as the type, and the honest way to set it is to measure rather than guess.
And if you screen mild, correction may do nothing for you. We benchmarked our own filters, the published daltonisation methods, and content-aware correction against observers simulated at mild, moderate and complete deficiency. At mild severity none of them separated a single colour pair that was previously confusable — while still shifting every other colour by the same amount they always do. Benefit scales with how impaired you are. The distortion does not.
That is a measurement under a model of colour vision, not a study of people, so it cannot tell you what you will experience — if a filter helps you read a particular chart, nothing here contradicts that. But it is the reason this page tells you to start low instead of selling you the strongest setting. The numbers are public →
IN YOUR BROWSER
Colorblind Corrector extension
Re-colours any page you visit. Pick a mode, set the strength, done. Makes no network requests and stores only your setting.
Install from the Chrome Web Store →
Install from Microsoft Edge Add-ons →
If you have taken a test on this site, the extension reads that result and sets your strength for you the next time you visit — no typing, no account.
Camera mode
Point your phone at the world and see it corrected live. Runs entirely on the device; nothing is recorded.
ON YOUR WHOLE SCREEN — WINDOWS
OpticQuiz Corrector (Windows)
Corrects everything on your display — games, PDFs, video, other applications — not only web pages. It sits in the system tray and you pick a mode from there.
Download OpticQuizCorrector.exe — 65 MB, Windows 8 or later.
It is a single file. Nothing to install, no .NET runtime needed, no administrator rights. Windows may warn that the publisher is unrecognised, because the build is not code-signed — a certificate costs money this project does not spend. You can read every line of its source and build it yourself if you would rather not trust a binary.
Its matrices are derived separately from the browser ones. Windows applies colour transforms in a different colour space, and the same numbers there produce a measurably worse correction — so it gets its own.
ON A SITE YOU OWN
The eye widget
Gives every visitor to your site a colourblind mode with a strength control. No build step, no dependency, no tracking.
<script src="https://opticquiz.com/widget/eye.js" defer></script>Or from npm, if you bundle:
npm install opticquiz-eyeIN YOUR OWN CODE
Check whether a palette survives colour blindness, fix one that doesn't, or simulate any of the three types. Byte-identical results across JavaScript and Python.
npm install opticquiz-cvd # JavaScript / TypeScript
pip install opticquiz-cvd # Python (matplotlib-friendly)
Or call it over HTTP with no install at all:
curl -X POST https://api.opticquiz.com/api/check \
-H "Content-Type: application/json" \
-d '{"colors":["#d7191c","#1a9641","#2166ac"]}'Everything for developers — API, VS Code, GitHub Action, MCP →
WHAT NONE OF THIS IS
These are aids, not a cure. They make colours easier to tell apart; they do not give you colour vision you do not have, and they are not a medical device or a treatment. Every correction here trades some colour accuracy for some separability, which is why the strength control exists and why lower is often better.
If you want to know what you actually have, print the notes page and take it to an optometrist. It is written for them, and it says plainly what a home screen cannot determine.