Skip to content
View Myndex's full-sized avatar


@w3c @thehighnibble @A11yReadTech
Block or Report

Block or report Myndex

Block user

Prevent this user from interacting with your repositories and sending you notifications. Learn more about blocking users.

You must be logged in to block users.

Please don't include any personal information such as legal names or email addresses. Maximum 100 characters, markdown supported. This note will be visible to only you.
Report abuse

Contact GitHub support about this user’s behavior. Learn more about reporting abuse.

Report abuse

Accurate Contrast
Using the APCA

INFO APCA Resources APCA Readability Criterion APCA/Main Repo
STATS version downloads  starsplain vanilla JS
APPS APCA Live Demo BPCA Live Demo CVD Simulator
Social twittermastodonlinkedinbluesky


  • Easy Intro to APCA? This is the simple, plain-language introduction to APCA that you've been looking for. This is an ideal place to start and is an easier version of WhyAPCA.

  • In an effort to pare down the mountain of material, this linktree is composed of the essential links, with the most basic at the top.

The Accessible Perceptual Contrast Algorithm

  • Basic Tool & Quickstart Docs The basic APCA demonstration tool with live font examples and general design guidance for designers and developers.
  • APCA Readability Criterion In depth guidelines for accomodating user needs regarding visual content, includes testing methods, conformance models, best practices, and more. Public Working Draft.

General Overview

  • Why APCA? This brief introduction into APCA describes how it solves the problems of WCAG_2 contrast. See Easy Intro to APCA? for the plain language version.
  • APCA in a Nutshell Basic overview for using APCA, including simple use-case based conformance levels. This is a bare bones version, for the deeper dive see APCA Readability Criterion
  • APCA FAQ APCA Frequenty Asked Questions (in development)
  • Easy Intro to APCA? This is the simple plain-language introduction to APCA that you've been looking for. This is a simpler version of WhyAPCA above.

APCA Technical Documentation

Social Media and Forums

Sciencey Stuff!

Maths! Theory! Vision Science! Photons on Parade!

For Developers

Related Repositories

Featured APCA Discussion Forum Threads

APCA Reviewed

A separate page comprised of the following listing of reviews is also available at APCA Reviewed, which is updated more frequently.

Independent Peer Reviews of APCA and
Third Party Comparisons vs WCAG 2

There are several independent researchers evaluating APCA, and additional third party comparitive reviews that include demonstrations of the functional superiority to existing methods. The first few listed below are technical reviews by peers evaluating the APCA math and methods, including journal published peer reviewed papers. Some in comparison to WCAG 2 contrast methods and guidelines.

APCA has been developed in the open for open peer review and discussion, and the reviews listed below were performed independently, the majority were completed without consulting the APCA developers. Reviews listed first are peer or academically oriented, and deal with theory, while reviews listed later are targeted more toward practicioners, designers, and developers.

Known Issues With WCAG 2 Contrast

Discussion with links to third party articles
written prior to the development of APCA

The problems of 4.5:1 as a target for a guideline is that it not only impact those with impairments, but impacts standard vision as well. WCAG 2 contrast SCs affect 100% of sighted users. The inherent problems with the WCAG 2 contrast math have been known for some time and widely critisized. Including studies by others showing that color insensitive types are not well served.

The WCAG 2 contrast specs often cause enough problems for designers that it is ignored and today, some 86% of websites are failing WCAG_2 contrast per an automated survey—though some of these failures are not due to poor actual accessibility, but due to the perceptual inaccuracies of WCAG_2 contrast.

The unfortunate end result is a grave distrust of the WCAG 2.x accessibility standards overall, despite the many other important aspects of those standards.

Myndex Color Resources

Myndex Web Apps

  • APCA Demonstrator The APCA contrast technology demonstrator—it's not as slick as a production tool, but presents the essential functions for design guidance.
  • Bridge-PCA Calculator Bridge-PCA or BPCA is a drop-in replacement for WCAG_2 contrast that is backwards compatible with the existing guideline, but is using APCA technology for improved readability.
  • Color Vision Deficiency Simulator This simulator demonstrates the way someone with a Color Vision Deficiency (incorrectly labeled "color blind") sees colors. This simulator uses the clinically accurate Brettel/Viénot model of CVD simulation for the primary (deuteranopia, protanopia, tritanopia) and there is an experimental blue cone monochromacy sim, based on the Brettel/Viénot concepts.

Featured Articles

On Readability & Contrast

  • The Realities And Myths Of Contrast And Color This popular article is an in-depth primer to vision, color, and contrast for design, written in the most plain language way possible. Features an emphasis on typography and readability needs. Published by Smashing Magazine.

  • Better reading on the web Published by UX Collective ( This article discusses and demonstrates the problems with automated testing and WCAG 2 contrast math, methods, and guidelines.

  • Published at Tangled Web (

    • Small Text is Medium’s Large Fail The Medium platform has a lot of good features going for it, yet it literally ignores visual accessibility. For a platform that is entirely based around readable content, one would think that it’d be close to State of the Art, instead of the State of Unreadable.
    • Hats off to ALL CAPS Myth-busting the misunderstandings regarding accessibility: are dyslexia fonts useful and the shift in using ALL UPPERCASE LETTERS for various text elements.
    • Getting the Wrong, Right? What does it mean to get something right, if the underlying foundation of that thing is ultimately wrong?
    • Busy Background Breaks Bulletin Examples of how to destroy readability by choosing the wrong image as a background. And also, how to fix it.
    • Please Stop Using Grey Text Debunking one of the worst myths regarding design contrast. THis article went viral in early 2022.
    • What's Red & Black & Also Not Read? Do the WCAG 2 Contrast Guidelines help users with color vision issues? While this is a widely held belief, the truth may surprise you.
    • A Contrast of Errors A look into the history of the WCAG 2 contrast guidelines and some of the problems created by them, and a discussion of the proposed replacement, the APCA (Accessible Perceptual Contrast Algorithm).

Additional Color & Contrast Related Articles

GitHub Gists

Mini articles on technical topics, with examples

Contrast & Color Gists

  • Three Part Series on WCAG 2 contrast problems with comparisons to perceptually uniform models.

  • COLORSPACES-The Primal Frontier A brief Look at the math that helps model how we see.

  • How Many Colors in a Bushel? Just "how many" colors are there? Is that even an answerable question?

  • Part I: For The Luv of Color An article comparing CIE Lab and Luv colorspaces.

  • Part II: Will Work for Color A follow-up article on working spaces and related considerations, including how ICC profiles may not be a great choice for web due to their inefficiency. Introduces the concept of "Web Working Spacelets".

  • colorPalette.js aka Kelly's 22 colors.

Related Threads & Comments (Legacy)

These were some of the larger, in-depth issue threads & posts created on GitHub including the infamous thread #695. These posts contain useful information and research. Some of the information here may be superseded as some of these threads date back to the beginnings of the contrast research project.

APCA—The Revolution Will Be Readable

Tech Articles NOT About Color

Society & Technology

  • Funny you mention Kodak and Xerox In this response to James Biber’s “Theranos, Polaroid and the legacy of dropouts”, I touch on the law of unintended consequences as has repeatedly manifested in the development of modern technology.
  • The Laws of Technodynamics An Illustrated Restatement of Thermodynamics in the Context of Applied Problem Solving Through Technology.
  • Climate Deniers Left & Right There are two kinds of climate deniers. Those that deny there is a problem, and those that deny the best way to fix it.
  • The Unbearable Cruelty of a Finite Existence At first glance, the concept of soul appears rooted in spirituality and religion. In reality the concept of soul is a manifestation of our ego. This very brief yet nihilistic essay leads to a concept on how to create a sentient AI.
  • Ending Polarized Politics Can a 200+ year old piece of math, and modern technology, fix this systemic problem in the US political system?
  • Election Fraud & Other Illusions How conspiracy theory websites gave rise to a widely spread disinformation campaign apparently aimed at voter suppression. And it was (and continues) to be a shocking example of using math and statistics to lie, by "baffling" with bull.
  • Modern Password Theory in a Nutshell Would it surprise you to know that fistsmash passwords aren't really more secure than one you can actually remember? You could say this is 0u+W!+h+h3_01d-InWithTheNew! — In other words, "Out With The Old - In With The New." It's a realistic discussion on password security, with a useful approach to reducing "crackability". HINT: we've all been doing it wrong, LOL. Article at
  • Improving SEO with Redirects Your server's case sensitivity and URL redirect strategies can affect your search ranking!

Other Tech Gists

Myndex on Other Sites

Myndex is top 3% on Stack Overflow!
profile for Myndex on Stack Exchange, a network of free, community-driven Q&A sites

The Lighter Side of Math & Photons...

The Art and Science of Applied Probability

In this career, I was using Applied Probability Methodologies for the Risk Assessment of short term ROI predictions related to high-variance cash-flow opportunities in finite-sized non-cooperative bidding groups where information is obliquely concealed as a function of multivariate strategies facilitating the predominately range-based tactics driven by randomized but nevertheless deterministic outcomes.

(…Sooo… this is more commonly known as Texas Hold ’Em Poker…)

For the record, Myndex is pronounced:

mind - ex
\ ˈmīn-ˌdɛks \

When George Eastman invented the word "Kodak" one of his criteria was that "it won't be mispronounced". I guess I missed that day. Ooops.

Just how many patent attornys does it take to rotationally engage a helical conducting thread of an illumination apparatus further comprised of a sealed, evacuated glass envelope containing two or more conducting filament holders which electrically connect and physically support a coiled electrically conducting but resistive filament, preferentially fabricated from a tungsten alloy, to the aforementioned helical threads, which further engage into a helical conducting receptacle, such that when an electrical power source of sufficient voltage and current is applied to the receptacle input conducting connectors, the voltage and current is henceforth transferred to the helical conducting threads of the illumination apparatus and thereto across the conducting filament holders and through said filament such that it shall be caused to incandesce and emit visible irradiance according to the laws of blackbody radiators?

The Answer as to how many: a plurality

Welcome to the very bottom of the page!

Here at the very bottom of the page, we dare to ask the question, "do two lights make a dark?"

Click for Answer

YES, two lights make a dark, if together they draw so much current they blow a fuse 💥.



    APCA (Accessible Perceptual Contrast Algorithm) is a new method for predicting contrast for use in emerging web standards (WCAG 3) for determining readability contrast. APCA is derived form the SAP…

    CSS 408 14

  2. apca-w3 apca-w3 Public template

    The APCA version, to be licensed for use with guidelines: W3/AGWG.

    JavaScript 142 16

  3. A11yReadTech/ARC A11yReadTech/ARC Public

    ARC • APCA Readability Criterion — a set of web-standard guidelines for text and non-text for use with the APCA contrast algorithm. Latest published version at this link:

    HTML 2 1

  4. bridge-pca bridge-pca Public

    A simplified version of the APCA math to bridge from WCAG_2 contrast math to the future, while being 100% backwards compatible with WCAG_2 contrast. By "backwards compatible" we mean if bridge-pca …

    JavaScript 12 3

  5. fancyfontflipping fancyfontflipping Public

    Fancy Font Flipping is a demo I first put up in CodePen to illustrate the issues with flipping the text color from black to white based on a given estimated background luminance.

    HTML 5

  6. deltaphistar deltaphistar Public

    𝜟𝜱✴︎ or Delta Phi Star is a variant method of determining lightness contrast, and a sibling of APCA and SACAM. It is a simplified version using easily invertible standardized maths, however it lack…

    HTML 21