Inactive Contrast?
Some comments on Giulia Alfarano’s great article on the subject.
Hi Giulia,
Great article. It is fascinating reading how users are working with guidelines we are developing. If you have questions about anything related, please feel free to post at our discussion forum at the APCA Discussion Forum
Some specific comments:
Regarding the warning button: if someone is red insensitive (protanopia) they will see that color darker, and as a result they will have increased contrast. Instead of Lc 50 they might see Lc 57. Other color vision types about the same as standard vision—but every individual is unique.
How much is enough
Regarding "does it look disabled enough" — this is a consideration. Accessibility is definitely NOT just about making things higher contrast. Contrast variation is needed to promote a visual hierarchy. This is its own separate a11y concern, particularly for coga.
To clearly separate a disabled button from an enabled one, I am leaning toward "ideally Lc 30 or more difference" though there are other good add-ins like desaturating, adding a grayness, Or maybe, increasing the outline to 4px, and at the same time lowering the outline contrast to Lc 15. These are experimental values, not official recommendations.
It’s about size
I don't know how big those buttons or text will be in the production UI, but per the article example looked heavy enough in weight to support lower than Lc 50. Between Lc 30 and Lc 45 is a good place for a disabled/inactive control that still needs to be somewhat perceived.
Contrast is more about spatial resolution than the colors, actually. Bolder and thicker is seen as higher contrast. Here’s an example, on the left is WCAG 3:1 (or APCA Lc 49) on the right is WCAG 7:1 (or APCA Lc 73). While the 7:1 is a little more contrasty, notice that the major change in perceived contrast is due to the line getting thicker or the font getting heavier. The fonts and lines themselves on left and right are identical.
Levels of Readability
The "non fluent" level is also known as "spot reading" per the research of Whittaker, Ian Bailey, and Lovi-Kitchin et alia. We have set it to support contrast impairments that supports reading by low vision. And the bonus is that all vision is helped. Lovi Kitchin determined that we need a contrast reserve of about 20 to 1 for best readability, spot needs three to one, and Lc 30 is three times a severe impairment.
Simulators
Not all colorblind simulators are made the same. Those based on the Brettel/Viénot Model are an ideal, if they are implemented correctly. Some others use math models that are inaccurate and can cause wrong conclusions. We have a free to use Brettel/Viénot sim at myndex.com/CVD/ and DaltonLens is also a good resource.
Thank you for reading,
Andy
Andrew Somers
Director of Research
Inclusive Reading Technologies, Inc.
W3C/WAI Invited Expert/WCAG3
Any opinions expressed are the author's and do not necessarily reflect those of the W3C or WAI.
