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Re: Colors and the WCAG

From: Charles McCathieNevile <charles@w3.org>
Date: Sat, 19 Oct 2002 17:24:55 -0400 (EDT)
To: Joe Clark <joeclark@joeclark.org>
cc: WAI-IG <w3c-wai-ig@w3.org>, <c.bottelier@iradis.org>
Message-ID: <Pine.LNX.4.30.0210191640170.15260-100000@tux.w3.org>

On Sat, 19 Oct 2002, Joe Clark wrote:

>> I far as I could find the WCAG 1.0 does mention that used
>> colors should be contrasting enough
>..which is virtually impossible for a layperson to estimate. Quickie
>question to the WAI: What exactly do other people see?

Not speaking for WAI, just myself, the answer is I don't know. I believe
(reaching into my memory, which tells me someone posted a proper reference to
this list once which I think is the basis for what I am saying) that having
something like a 50% or greater difference in values of saturation and
brightness, combined with a 90-degree difference in hue, provides enough
contrast that most sighted people can usefully distinguish things. Of course
there are some people who use black and white only, and large size (at least
there are some friends of mine who do this. I suspect they are not the only

Good question by the way.

>> On the Internet I see a lot of pages, and the tools like
>> FrontPage and DreamWeaver tend to do it, is to specify
>> the bgcolor as white but not any of the other colors. Should
>> the WCAG not mention (priority 1 of 2 perhaps) that when
>> specifying the color of 1 element, all the other colors
>> _MUST_ be specified also. And that if _ALL_ the colors
>> specified are the default colors their MAY not be specified
>> at all (priority 3)?
>No, because the number of real-world browsers that cannot understand
>CSS is so very small that HTML-only techniques are no longer
>You *can* set just the background on, say, html or body and then set
>the foreground on other elements.
>Cascading, remember?

If you set foreground colours but not background colours you haven't
specified any contrast, and have therefore failed the checkpoint, in my
opinion. But Joe is right that you don't need to do this for every element -
you can use the inheritance of properties if you have set a background
globally and foregrounds locally or vice versa.


Received on Saturday, 19 October 2002 17:24:57 UTC

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