11

It has been claimed (for instance, in a paper presented at a W3C symposium, by UX Movement, on the audioeye.com blog, in a medium.com post with a handful of claps, and perhaps most notably by the British Dyslexia Association) that, when designing a web page, you shouldn't use pure black text (#000000) on a pure white background (#ffffff) because it is harmful for readers with dyslexia. The top-voted answer on UX.SE to a question about the usability of this color combination is also arguing that it is harmful to dyslectic readers.

However, not all of these sites give references, some of them use the same references, some of them use references that are not from peer-reviewed publications, and some of them use references that are not available anymore.

The paper from the W3C symposium (sometimes incorrectly referenced as a "W3C report") appears to be the closest to a scientific publication, and it is the one used as a reference in the audioeye.com and medium.com blogs. It's a symposium contribution, though, and I don't know how rigorous the review standard was. In the paper, the authors cite two websites which are now off-line as sources that pure black on pure white is harmful for dyslectic readers, one of which (Bradford 2011) is the reference given in the UX Movement text. The actual data that the authors used came from another conference paper by them, so that reference is also not really helpful.

In sum, although the claim that black on white is harmful for readers with dyslexia appears to be common knowledge in the web design community, I couldn't find strong evidence that this claim is based on solid empirical research. Note that this is not about the aesthetics of this color combination, or whether a color combination where the contrast is too low is difficult to read. This question is only about the claim that pure black on pure white is difficult to read for dyslectic readers.

So, is this particular claim true?

7

I'm not convinced the 2012 W3C symposium paper is interpreted properly. Here's a quote from a 2015 paper by the same authors (Rello & Baeza-Yates):

This paper presents the following main contributions:

[stuff about font size etc., then]

– Black text on white background instead of using grey scales for the text is significantly preferred by people with and without dyslexia.

– White text on black background instead of using grey scales for the background is significantly preferred by people with and without dyslexia

So it looks to me it's the maximization of contrast that matters. I'm not sure about the black on white vs white on black (right now).

Also from that paper I gather there's not much research on the topic of color schemes for dyslexics (there's much more on font sizes and spacing). The only color-related research from a different group cited in there was Kurniawan and Conroy (2007). And here's what they found (p. 268) studying a group of 5 dyslexics (and a number of controls):

When asked about their most effective colour scheme, each student with dyslexia provided a slightly different answer. Some said that they did not have any problem with black and white as long as the paragraphs were short and the page had plenty of white spaces. Some preferred “any dark coloured text” on baby pink background, dark blue on cream, and black on “any light coloured background.” Not surprisingly, all the students without dyslexia preferred black and white. The students without dyslexia who were given the passages in dyslexia-friendly colours stated that they felt very dizzy reading the passages on coloured screen, and they had to use their fingers to follow the sentences because of that. Some suggested that this might be the main cause that their reading speeds were lower than those of the other groups.

Full ref for the latter paper: Kurniawan, S., Conroy, G.: Comparing comprehension speed and accuracy of online information in students with and without dyslexia. Advances in Universal Web Design and Evaluation: Research, Trends and Opportunities, Idea Group Publishing, Hershey, PA pp. 257–70 (2006)

And I think the recommendation for colored presentation is based on a particular cause of dyslexia (p. 262 in Kurniawan and Conroy):

Tinted lenses and coloured overlays. Some people with dyslexia suffer from a condition called Meares-Irlen syndrome. Text or symbols become blurred or indistinguishable soon after reading begins. This is particularly the case when reading information presented in high contrast, such as black text on a white background. The condition varies in its severity, but in most cases it can be improved with the use of simple coloured overlays (placed over pages or computer screen) or tinted lenses.

I'm not sure how many dyslexics suffer from Meares-Irlen syndrome to make the recommendation universal... Also, perusing the Wikipedia page on the latter, I gather it's "very rare" and colored overlays might not actually work to alleviate it; the latter finding is from a 2011 paper (Ritchie et al.) in a medical journal. And 2014 review mentions that paper and other recent negative findings:

Some recent studies failed to find statistically significant effects of colored overlays. Ritchie et al. (2011) had shown that, in the short period, colored overlays do not speed reading up compared to non-colored overlays, whether or not the participants have a diagnosis of visual stress. Ritchie et al. (2012) had shown that – compared to a control condition – not even one year of use of colored overlays results in an increase in reading speed and accuracy. Henderson et al. (2013) had shown that despite the fact that often dyslexic individuals do experience stronger visual stress than controls, neither dyslexics nor controls benefit from the use of colored overlays.

However its conclusions are a bit more nuanced:

Whether colored overlays help reading or not seems at least controversial: although initial evidence was indeed provided, more recent studies both highlight the methodological issue of previous studies and show that colored overlays do not help reading (Ritchie et al., 2011, Ritchie et al., 2012; Henderson et al., 2013), On the ground of contradictory findings as these, the [American Academy of Pediatrics (AAP), 2009] has claimed that there is not empirical evidence toward the efficacy of colored overlays in reading, reading acquisition, or dyslexia, and did not recommend their use.

However, the participants in the studies of Ritchie et al. (2011); Ritchie et al. (2012) were non-dyslexic children, and in the study of Henderson et al. (2013) they were adults, whereas it has been shown that effects of colored overlays are more easily found with dyslexic children (Singleton and Trotter, 2005; Singleton and Henderson, 2007). Whether or not, at least in some conditions, colored overlay works does not seem to be a settled issue. Thus, although from one side, given these contradictory findings, a precautionary, prudent position – as that of the Academy of Pediatrics – on the use of colored overlay seems desirable, especially in clinical or educative contexts, from another side, given that some evidence that the colored overlays work exists, concluding that colored overlays proved not worth in allaying reading problems is premature and, possibly, incorrect.

The lack of efficacy of color overlays is also mentioned in a summary of the book "The Dyslexia Debate", p. 4. That book has a lengthy review in one of main neuroscience journals, namely in BRAIN. While the review does take issue with a number of tenets of the book, it doesn't challenge much the book's take on treatments, so I conclude that the colored overlays not working much is a fairly valid conclusion, although possibly encumbered by diagnostic difficulties with dyslexia subtypes. At the very least, the recommendation to use colored overlays for all dyslexics seems unsupported.

Going back to Rello and Baeza-Yates (2015), they mention that some Firefox extension that allows extensive customization:

Santana et al. [90] developed the Mozilla Firefox extension Firexia, a tool that allows readers with dyslexia to customize websites to improve readability. They tested Firexia with four users and found that readers with dyslexia appreciate customization. The customization settings included in Firexia are based in previous user studies and recommendations. They include font type, font size, color, character spacing, line spacing and column width.

So probably the best technological recommendation (until the science of dyslexia [and its treatments] gets sorted out) is to do something like that.

  • Really nice answer, interesting to see this isn't exactly set in stone.. – colsw Jun 27 '18 at 7:44
  • I liked this answer more at an earlier stage before you added the research on color overlays – I made it quite clear that my question is only about the pure black on pure white issue. Still, the first part is a good, well-researched answer to that. – Schmuddi Jun 29 '18 at 20:54

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