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comments on colour SC

From: Web Usability <rhudson@usability.com.au>
Date: Wed, 21 Dec 2005 16:53:36 +1100
To: "Public-Comments-Wcag20" <public-comments-wcag20@w3.org>
Message-ID: <GGEEINFOLDEIIBPBECEMOECCCGAA.rhudson@usability.com.au>

H1 Working Group

Many thanks for all your work.

Some comments relating to the Success Criterion concerned with the use of
colour follow:

Comments on colour differentiation

I have worked with a number of people with impaired colour vision who
encounter significant difficulties differentiating between the colours that
are sometimes used on websites. I have also noticed that as people get older
their ability to perceive colours and differentiate between colours seems to

In WCAG 1.0, Checkpoint 2.1 is a Priority 1 requirement for all information
that is conveyed with colour to also be available without colour. However in
my opinion the needs of people who have problems differentiating between
certain colours is not adequately met by Checkpoint 2.1, which is a peculiar
mix of Priority 2 and Priority 3 checkpoints.

WCAG 2.0 Success Criterion 1.3.2 appears to be a part replacement for the
old Checkpoint 2.1 and is a Level 1 criterion. However, there is also a
Level 2 Criterion that deals with the communication of information via

WCAG 2.0 Success Criterion 1.3.4 (Level 2) states:
“1.3.4 Any information that is conveyed by color is visually evident when
color is not available.”

The “Understanding WCAG 2.0 (Working Draft 23 November 2005)” document,
provides the following advice in relation to intention of this criterion:

“The intent of this success criterion is to ensure that all users can access
information that is conveyed by color.

This success criterion is similar to 1.3.2. However where 1.3.2 allows color
information to be made accessible directly OR via assistive technology —
this success criterion (1.3.4) is focused on people with color anomalies who
do not use assistive technologies. Hence this success criterion is focused
on seeing that information conveyed via color is available without color and
without requiring the person to use any assistive technologies.”

I am unclear as to why a distinction is being made between people who are
unable to perceive colour and use an assistive technology and those who are
unable to perceive colour but don’t use an assistive technology.  Surely the
point is, that if someone cannot access information because of their
inability to perceive colour then that information is effectively
inaccessible to them and an alternative should be provided.

In my opinion Success Criterion 1.3.4 should either be a stand-alone Level 1
Criterion, or incorporated into Success Criterion 1.3.2.

The issue of ensuring there is enough contrast between text (foreground) and
its background appear to be addressed in the following Success Criterion for
WCAG 2.0 Guideline 1.4:

“1.4.1 Text or diagrams, and their background, must have a luminosity
contrast ratio of at least 5:1. (Level 2)

1.4.3 Text or diagrams, and their background, must have a luminosity
contrast ratio of at least 10:1. (Level 3)”

The spread of this requirement over two Success Criterion Levels appears to
be an effective way of recognising the fact that the higher the contrast
ratio the more likely the information will be accessible to a greater number
of people with impaired colour vision.

However in my opinion, greater importance should to be given to the needs of
people who have difficulty distinguishing foreground text from its
background. I would urge the working group to consider changing the success
Levels for these criteria. That is the Success Criterion for 1.4.1 should be
Level 1, and for 1.4.3 it should be Level 2.

Once again, thanks and best wishes for the new year.


Roger Hudson
Received on Wednesday, 21 December 2005 05:54:10 UTC

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