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RE: Colour blindness and accessibility

From: Christophe Strobbe <christophe.strobbe@esat.kuleuven.ac.be>
Date: Wed, 30 Apr 2003 11:11:53 +0200
Message-Id: <>
To: Nick Kew <nick@webthing.com>, "Matthew R. Moore" <mrmoore@truman.edu>
Cc: Lois Wakeman <lois@lois.co.uk>, w3c-wai-ig@w3.org, immelie@hotmail.com


At 08:13 30/04/2003, Nick Kew wrote:

>On Tue, 29 Apr 2003, Matthew R. Moore wrote:
> > Another example along the same vein that we discussed is when form
> > validators change
> > the color of the text on the form to a certain color (i.e. red) and say 
> that
> > "fields in
> > red must be completed" - if someone can't distinguish red for some reason,
> > how can
> > they know that the form field is required?
>Now that on the other hand is easy, and serves to demonstrate the
>inherent accessibility of HTML/CSS (when not abused).  The author
>specifies in CSS
>.mandatory      { color: red ; }
>and the colour-blind user has an instant override, specifying a user
>stylesheet that distinguishes mandatory fields in a manner that is
>accessible to him.

This also demonstrates that using HTML and CSS can result in mixing up 
structure and presentation (cf. Jukka Korpela's article on 
http://www.cs.tut.fi/~jkorpela/styles/harmful.html). Because form elements 
in HTML do not have an attribute called "mandatory" or "required", you 
create a new type of field with class="mandatory" or class="required" or 
whatever comes to mind. This means that the user has to check your HTML 
code to find out which class selector they should at to their stylesheet. 
So they would have to write
.mandatory, .required, .req { color: red;}
and this is just for web sites in English. Some people (like me) read web 
sites in other languages.

Stylesheets are not that easy to reuse on different sites. You can see this 
when you test this with the different stylesheets from the W3.org homepage 
redesign contest (cf. http://w3mix.web-graphics.com/win.php): I downloaded 
the stylesheets and linked them to a local copy of the W3C home page, which 
gave bad results; interchanging the stylesheets of the different entries 
does not work either.

Christophe Strobbe


Christophe Strobbe
K.U.Leuven - Departement of Electrical Engineering - Research Group 
on  Document Architectures
Kasteelpark Arenberg 10 - 3001 Leuven-Heverlee - BELGIUM
tel: +32 16 32 85 51
tel GSM: +32 473 97 70 25
fax: +32 16 32 19 86
Received on Wednesday, 30 April 2003 05:11:49 UTC

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