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Re: Notes from Matt McMahon presentation on color blindness at UW

From: Joe Clark <joeclark@joeclark.org>
Date: Wed, 14 Jan 2004 14:42:23 -0500 (EST)
To: WAI-GL <w3c-wai-gl@w3.org>
Message-ID: <Pine.BSO.4.53.0401141434210.18221@mail.veldt.ca>

> I am using a Macintosh G3 desktop computer and realize that colors across
> browsers, operating systems and monitors "may" vary with regard to perceived
> colors.  But, RGB values, if used correctly, should render the same value,
> regardless of a users perceived notion of color.

This seems contradictory. The RGB value (if you're using that colourspace)
is a fixed thing, but it is indeed the manifestation and perception that
count. And those two things will vary, especially for older people with
acquired colour deficiency, as through yellowing of the iris.

> In relationship to checkpoint 1.6, we really are not concerned about a users
> ability to see and identify color - we are concerned about their ability to
> see text that is presented over background colors.  The Brewer Palette and
> her use of color spaces may be a valuable resource.

Well, I coined the term "Brewer Palette," I documented her work for a lay
Web-design audience, and the ColorBrewer tool is not really useful for Web
design per se.

(Hi, Chris!)

In the usual course of events, it doesn't matter how a colour is perceived
by the Web visitor. The goal is to avoid confusion or illegibility. It is
quite possible to use confusable colours (as red and green or blue and
green and the analogous hues along those colour lines) in unconfusing
ways. It's up to the designer to make reasonable choices, and, if there is
a likelihood of difficulty in reading, to provide stylesheet-switchers or
a similar mechanism. Failing that, it's up to the reader to take matters
into his or her hands and employ, for example, a user stylesheet.

An author who didn't want to go to all that trouble, but who still wanted
to use a variety of colours, could simply use the Brewer Palette, which
contains hues that even colour-deficient people (at least with congenital
colour deficiencies-- it hasn't been tested with acquired deficiencies to
my knowledge) can tell apart and whose names everyone agrees on.

I think this is now my second year of telling the Working Groups the same
things over and over and over again, including at the Toronto f2f, and
simply having it all ignored. When *are* you going to cut that out?


  Joe Clark  |  joeclark@joeclark.org
  Author, _Building Accessible Websites_
  <http://joeclark.org/access/> | <http://joeclark.org/book/>
Received on Wednesday, 14 January 2004 14:40:22 UTC

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