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Re: BODY Colors

From: Leonard R. Kasday <kasday@acm.org>
Date: Fri, 26 Mar 1999 17:53:16 -0500
Message-Id: <3.0.32.19990326175313.010bb208@pop3.concentric.net>
To: "Chris Ridpath" <chris.ridpath@utoronto.ca>, "WAI ER IG List" <w3c-wai-er-ig@w3.org>
> 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

http://www.temple.edu/inst_disabilities/piat/webcheck/

search down the page for "color"

For more explanation, see 

http://www.lighthouse.org/color_contrast.htm


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.

Len



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?
Chris    



-------
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
kasday@acm.org        
(215} 204-2247 (voice)
(800) 750-7428 (TTY)
Received on Friday, 26 March 1999 17:51:51 GMT

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