What is a Color Blindness Checker?

A Color Blindness Checker is a tool that simulates how web pages appear to people with various types of color vision deficiency (CVD). It applies scientifically-derived color transformation matrices to render the page as seen by someone with protanopia, deuteranopia, tritanopia, or other forms of color blindness. This helps designers and developers create more accessible, inclusive web experiences.

How does this live URL checker work?

Simply enter any website URL and select a color blindness type. Our tool loads the page in a sandboxed iframe and applies precise SVG feColorMatrix filters that map RGB values to simulate each type of CVD. You can switch between 7 different simulation types and compare side-by-side with the original page. The filters are based on established LMS color space transformation research.

What are the different types of color blindness simulated?

• Protanopia – Red-blind: Missing red cone photopigments. Reds appear dark or brownish.
• Deuteranopia – Green-blind: Missing green cone photopigments. Greens appear beige or brown.
• Tritanopia – Blue-blind: Missing blue cone photopigments. Blues appear greenish, yellows disappear.
• Achromatopsia – Total color blindness: No color perception, only shades of gray.
• Protanomaly / Deuteranomaly / Tritanomaly – "Weak" forms where cones are present but altered, resulting in milder color confusion.

How common is color blindness?

Color vision deficiency affects approximately 8% of males (1 in 12) and 0.5% of females (1 in 200) of Northern European descent. Red-green color blindness (protan and deutan types) accounts for about 99% of all cases. Tritanopia is much rarer, affecting roughly 1 in 10,000 people. Achromatopsia is extremely rare, affecting about 1 in 30,000 people.

Why should I test my website for color blindness accessibility?

With over 350 million people worldwide experiencing some form of color blindness, ensuring your website is perceivable by all users is both an ethical obligation and often a legal requirement under accessibility standards like WCAG 2.1. Poor color contrast or reliance on color-only cues (like red/green error states) can make your site unusable for a significant portion of your audience. Testing helps you identify and fix these issues before they impact real users.

What are WCAG guidelines for color accessibility?

The Web Content Accessibility Guidelines (WCAG) 2.1 require that color is not the sole means of conveying information (Success Criterion 1.4.1). Additionally, text must maintain a contrast ratio of at least 4.5:1 for normal text and 3:1 for large text (SC 1.4.3). This tool helps you visually verify that your design works for color-blind users and identify elements that may need alternative visual cues like icons, patterns, or text labels.

Can I use the side-by-side compare mode?

Yes! Click the "Side-by-Side Compare" button to view the original page next to the simulated version. This makes it easy to spot exactly which UI elements lose contrast or become indistinguishable. The compare mode is especially useful for reviewing call-to-action buttons, form validation states, charts, maps, and navigation elements. On mobile devices, the two views stack vertically for comfortable scrolling.

Are the color blindness simulations accurate?

The simulations use feColorMatrix transformations based on peer-reviewed research in color vision science. While they provide a highly accurate approximation, individual experiences of color blindness can vary. The matrices map RGB values through LMS color space conversions that model the spectral sensitivity of human cone cells. For protanopia and deuteranopia, the simulations are considered very reliable. Tritanopia simulations are slightly less precise due to the rarity of the condition and limited research data.

Why won't some websites load in the preview?

Many major websites set the X-Frame-Options or Content-Security-Policy HTTP headers to prevent their pages from being embedded in iframes. This is a security measure against clickjacking attacks. If a site won't load, try testing with your own website (where you can configure these headers), or use our preset URLs which are known to allow embedding.