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Re: Colour contrast and blue light filters


From: Patrick H. Lauke
Date: Jan 31, 2019 5:45AM

On 31/01/2019 12:34, Pat Reynolds wrote:
> We are working on a major overhaul of colours on all our sites, to make
> them AA compliant. Does anyone know how these filters might impact on
> accessibility, and what we might do to mitigate that?

I'm assuming that you mean you're going to ensure the colour contrast
ratios of all foreground/background colour combinations are AA compliant
- minimum 4.5:1 for "regular" text / 3:1 for "large" text (and, if doing
WCAG 2.1, also minimum 3:1 for meaningful non-text content).

It will depend on the specific blue light filter used (as I don't think
there's any particular standard way in which these work), but while
these filters generally result in a duller/less pronounced/lowered
contrast overall, following at least the minimum WCAG contrast ratios
should still result in a strong-enough contrast. To be on the safe side,
stronger contrasts (not just trying to squeak past the 4.5:1 ratio, for
instance) will be better and safer. If it's a major concern, you can
always run a simulated blue filter and test the contrast ratios AFTER
the filter was applied, and tweak to ensure that they're strong enough
even when the filter is on.

Of course, with regards to WCAG, you should also ensure that color alone
is not used as an indicator/to convey meaning, as this may also
otherwise cause problems for users that run a blue filter.

Patrick H. Lauke

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