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Re: Specifying foreground and background colors

From: Charles McCathieNevile <charles@w3.org>
Date: Tue, 13 Jun 2000 22:06:30 -0400 (EDT)
To: Wendy A Chisholm <wendy@w3.org>
cc: w3c-wai-gl@w3.org, w3c-wai-ua@w3.org, w3c-wai-er-ig@w3.org
Message-ID: <Pine.LNX.4.20.0006132203310.13676-100000@tux.w3.org>
The accessibility requirement is to have sufficient contrast. With only one
colour specified, there is no known contrast.

This is not primarily a UA issue (in my opinion), but an Authoring issue. It
is possible for a UA to repair it, of course, but it has to do so by
guesswork (although it is likely to de a better job than a person in many
instances. That means that when this repair strategy is automatically
implemented in Authoring tools we may get an overall improvement - depends on
the algorithms and interfaces...)

Cheers

Charles

On Tue, 13 Jun 2000, Wendy A Chisholm wrote:

  At 12:59 AM 6/10/00 , Charles McCathieNevile wrote:
  >Assuming a particular colour combination is a user's default and that
  >therefore it is only necessary to specify colours for things that are not the
  >default is a mistake.
  >(particularly for accessiblity reasons they may choose
  >something else, although there may be other reasons. I don't know that it is
  >a reason not to include the technique, as the way to specify thinigs
  >correctly.)
  
  My main question is not "should we include this as a technique."
  
  Rather, my question is, "what is the accessibility rationale for this 
  technique."  I did not see any, thus did not include any in my proposal.
  
  I think the rationale is "good design."  Regardless of whether I choose a 
  high-contrast background and foreground color combination (white and dark 
  red), if the user only selects a foreground color (white) current user 
  agents will not select a high contrast background color.  They will display 
  the author set background color (white) and the user set foreground color 
  (white).  The user will have to select a foreground color as well.  In some 
  browsers, the user could select "high-contrast mode" where the browser 
  selects both the foreground and background colors.  For example, yellow 
  text on a black background.
  
  >Maybe we should ask the ER or UA groups to look in more detail at the issue
  >of ensuring contrast? Most User Agents allow a choice of colours, although
  >most do not automatically pick a contrasting colour where there is a conflict
  >or semi-specified colour scheme.
  
  I think this is a UA issue and have CC'ed the UA working group.  Chris 
  Ridpath recently published results of a color study, so I have CC'ed ER as 
  well.  Refer to the techniques for Checkpoint 2.2 in the 26 April 2000 
  working draft of AERT [1].
  
  Since there do not appear to be any objections to my proposed edit of the 
  CSS techniques module, I will make the appropriate changes.
  
  --wendy
  
  [1] http://www.w3.org/TR/AERT#color-contrast
  
  
  >On Thu, 8 Jun 2000, Wendy A Chisholm wrote:
  >
  >   I have two questions in relation to this issue:
  >   1. will user agents automatically make adjustments for background or
  >   foreground color if the author specifies a good combination but the user
  >   only specifies one or the other (foreground or background but not
  >   both)?  It is my experience that user agents do not.
  >
  >   2. I intend to include this in the techniques document, but would like a
  >   rationale.  It seems that the rationale is good design rather than an
  >   accessibility issue since the answer to the first question seems to be 
  > "no."
  >
  >   If there is no disagreement, I propose editing section 5 (Colors) of the
  >   CSS techniques module to read:
  >   <blockquote>
  >   Use these CSS properties to specify colors:
  >   'color', for foreground text color.
  >   'background-color', for background colors.
  >   'border-color', 'outline-color' for border colors.
  >   For link colors, refer to the :link, :visited, and :active pseudo-classes.
  >
  >   Note that when a background color is specified, specify a high-contrast
  >   foreground color and vice-versa.
  >
  >   Ensure that information is not conveyed through color alone. For example,
  >   when asking for input from users, do not write "Please select an item from
  >   those listed in green." Instead, ensure that information is available
  >   through other style effects (e.g., a font effect) and through context
  >   (e.g,. comprehensive text links).
  >   For instance, in this document, examples are styled by default (through
  >   style sheets) as follows:
  >   They are surrounded by a border.
  >   They use a different background color and also specify a high-contrast
  >   foreground color.
  >   They begin with the word "Example" (or "Deprecated Example".
  >   They also end with the phrase "End example", but that phrase is hidden by
  >   default with 'display: none'. For user agents that don't support style
  >   sheets or when style sheets are turned off, this text helps delineate the
  >   end of an example for readers who may not be able to see the border around
  >   the example.
  >   </blockquote>
  >   --wendy
  >
  >   At 12:59 AM 6/7/00 , Wendy A Chisholm wrote:
  >   > From the issues list:
  >   >
  >   ><blockquote>
  >   >Issue raised by: Philip Newton - 7 May 1999
  >   >Issue:
  >   >If the author specifies a background color, they should also specify the
  >   >foreground color (and vice versa), otherwise if the user has selected a
  >   >particular foreground color that does not contrast well with the author's
  >   >background color, the page will be unreadable.
  >   >
  >   >Proposed Resolution
  >   >While the user should be able to adjust preferences on the user agent, it
  >   >is good design. Therefore, it seems to make sense to discuss in 
  > techniques doc.
  >   ></blockquote>
  >   >
  >   >Even if the author selects both a background and text color, if the user
  >   >selects a foreground color that does not contrast well with the author's
  >   >background color then what can you do?  If the user only selects one 
  > color
  >   >but the author has selected both foreground and background, the user 
  > agent
  >   >will not automatically use colors that contrast well, will it?
  >   >
  >   >I agree this is good practice but I am not sure that this increases
  >   >accessibility.
  >   >
  >   >Thoughts?  Do people have experiences that support the proposal?  Does
  >   >someone have a good test page for this?
  >   >--wendy
  >   >--
  >   >wendy a chisholm
  >   >world wide web consortium
  >   >web accessibility initiative
  >   >madison, wi usa
  >   >tel: +1 608 663 6346
  >   >/--
  >
  >   --
  >   wendy a chisholm
  >   world wide web consortium
  >   web accessibility initiative
  >   madison, wi usa
  >   tel: +1 608 663 6346
  >   /--
  >
  >
  >--
  >Charles McCathieNevile    mailto:charles@w3.org    phone: +61 (0) 409 134 136
  >W3C Web Accessibility Initiative                      http://www.w3.org/WAI
  >Location: I-cubed, 110 Victoria Street, Carlton VIC 3053
  >Postal: GPO Box 2476V, Melbourne 3001,  Australia
  
  --
  wendy a chisholm
  world wide web consortium
  web accessibility initiative
  madison, wi usa
  tel: +1 608 663 6346
  /--
  

--
Charles McCathieNevile    mailto:charles@w3.org    phone: +61 (0) 409 134 136
W3C Web Accessibility Initiative                      http://www.w3.org/WAI
Location: I-cubed, 110 Victoria Street, Carlton VIC 3053
Postal: GPO Box 2476V, Melbourne 3001,  Australia 
Received on Tuesday, 13 June 2000 22:06:32 GMT

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