APCA is dead
Alas the complicated, but also exciting, APCA is no longer a part of WCAG3. APCA (or Accessible Perceptual Contrast Algorithm) had confronted known flaws in the existing colour contrast formula, quoting from Myndex (Who I think is Andrew Sommers) in Why APCA as a New Contrast Method?:
WCAG 2.x contrast, SC 1.4.3, and the related understandings and guidelines, were born in an era before smart phones and iPads, when displays were mostly old-school CRT type and websites used core web fonts. But that was a decade and a half ago. Today the contrast guidelines are in need of a complete overhaul due to the massive changes in computer display technology, web content, CSS functionality, and advances in vision science since 2005/2008, when WCAG 2.x was first introduced.
There are a number of reasons that WCAG 2.x contrast is faulty, one of which is the binary pass/fail nature of the SC for a property that does not apply in a binary way across perception nor impairments. Humans are not binary computers, and it is important to understand the non-linear aspects of perception, and to set guidelines that correctly model perception as opposed to “brute forcing” arbitrary values that ultimately do more harm than good.
Not sure what happens to these flaws that APCA was addressing, but it unfortunately it seems that it is not happening.
Going to leave a few more links here for interest’s sake:
- Better reading on the web by Andrew Sommers
- A wonderful twitter thread by Dan Hollick, that I’ve chosen to archive as a PDF. There is a link to the original thread in there if you’re so inclined to visit
- My old post about APCA - APCA tools & resources