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Re: BODY Colors

From: Chris Ridpath <chris.ridpath@utoronto.ca>
Date: Tue, 30 Mar 1999 08:57:34 -0500
Message-ID: <006901be7ab5$42fb7e80$b040968e@WILDDOG.ic.utoronto.ca>
To: "WAI ER IG List" <w3c-wai-er-ig@w3.org>, "Leonard R. Kasday" <kasday@acm.org>

Thanks for the suggestions. I had a look at your site and the lighthouse
site and picked up some good ideas.

The problem now is how do we quantify the colors. On your computer, the
colors are represented by 3 values (red, green and blue) and the values
range from 0 to 255. So what represents a poor visibility red? What values
make up a 'dark' background?

I have a small test program that allows you to modify the background and
text colors and view their RGB values. I'll send you the program in a
following message. If anyone else is interested in the program, let me know
and I'll send it to you.


-----Original Message-----
From: Leonard R. Kasday <kasday@acm.org>
To: Chris Ridpath <chris.ridpath@utoronto.ca>; WAI ER IG List
Date: March 26, 1999 5:52 PM
Subject: Re: BODY Colors

>> What makes a good  contrast? Just brightness? Just color difference? >
>What about link  colors?
>Color makes a difference.  Generally, disabilities reduce sensitivity to
>the extremes of the light spectrum, viz. red and blue.  This implies
>   1.There shouldn't be any red or blue on darker backgrounds, since the
>red and blue will get darker and reduct contast.
>   2.There shouldn't be any green, yellow, cyan on lighter backgrounds
>(because lighter backgrounds will contain some red and blue and become
>darker, thus reducing contrast.  This is a bit of a simplification, since
>theoretically dark green on light green is OK.)
>For examples of these see
>search down the page for "color"
>For more explanation, see
>I don't know of any good quantitative procedures, especially for people
>with vision impairments.  So as a rule of thumb, follow the above rules and
>make contrast subjectively very high for normal vision.
>Note that simply viewing in some arbitrary monochrome does NOT constitute a
>good test, since the conversion to monochrome does not necessarily show
>what would happen with visual impairments.
>Also, note that color contrast is more important for images than for BODY
>color, since users can override body and font color in their browsers.  But
>they can't override colors in images.
>This is another reason that background images are a problem. For example,
>if a peson chooses light text and dark BODY, then there's a big problem if
>the page has a light background image.
>So a tool should look at images too.
>At 02:40 PM 3/24/99 -0500, Chris Ridpath wrote:
>The WAI guidelines (4.2) state:  Use foreground and background color
>combinations that provide sufficient  contrast when viewed by someone with
>color deficits or when viewed on a black  and white screen.  In our
>A-Prompt program, we check the BODY  element for background/text colors and
>if they are set we warn the user. But  some color combinations are OK
>(white background, black text) and we shouldn't  warn the user about them.
>We would like to make the program smart enough so that if it  sees a large
>contrast between the background and text colors, it will NOT warn  the
>user. We're looking for ideas on how this could be done. What makes a good
>contrast? Just brightness? Just color difference? What about link  colors?
>Leonard R. Kasday, Ph.D.
>Universal Design Engineer, Institute on Disabilities/UAP, and
>Adjunct Professor, Electrical Engineering
>Temple University
>Ritter Hall Annex, Room 423, Philadelphia, PA 19122
>(215} 204-2247 (voice)
>(800) 750-7428 (TTY)
Received on Tuesday, 30 March 1999 09:00:23 UTC

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