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Non-text colour contrast sub-topic

From: Alastair Campbell <acampbell@nomensa.com>
Date: Sat, 19 May 2018 23:02:57 +0000
To: Michael Gower <michael.gower@ca.ibm.com>
CC: "w3c-wai-gl@w3.org" <w3c-wai-gl@w3.org>
Message-ID: <AM5PR0902MB20020B07DA979946C2155FB7B9970@AM5PR0902MB2002.eurprd09.prod.outlook.com>
Hi Michael,

After the call on Thursday I wanted to describe one of the issues discussed, in preparation for Tuesday. I think it would help to talk through some concepts and examples in advance.

For context, as part of the proposed version [1] I had removed a section under "Note on SC 1.4.1 Use of Color" from the current version [2]:
> "Relative luminence: If the selected and unselected states of an object do vary only by color, this is still acceptable to meet 1.4.1 so long as the luminosity contrast ratio between the selected and unselected colors differs by at least 3:1 (and each color also meets 3:1 contrast with the background adjacent to the control, in order to meet 1.4.11)."

The reason I had removed it is because I saw it conflicting with another concept, where is says:
>  "the visual effects which indicate state, such as whether a component is selected or focused, must also provide the minimum 3:1 contrast with the background adjacent to the component."

In discussions in the LVTF something we've been very conscious of is the three-way contrast conundrum, i.e. if you need contrast between three colours you have a very limited range and it impacts the design in quite significant ways.

Overall, we have defined the contrast needed as between the components boundary and it's surroundings, so I'm very concerned that if a link/button uses a border/background to indicate state, it will not be able to do so effectively and contrast with both itself and surroundings.

Where I've applied 1.4.1 Use of Color before is similar to its understanding document [3], so "visual means of conveying information" is things like changing the colour of required form fields, things that are more significant than the hover/active state of a component.

Focus is one thing (and called out in the techniques of 1.4.1), but the other states defined in 1.4.11 expand that a lot (e.g. select, press, visited), and I'm not comfortable using this combination of SCs to increase the scope beyond the intent of both.

Looking at it again, I'm think the whole 1.4.1 section revolves around this point, so it's probably best to remove it all, or keep it all.

Am I missing something?



1] https://rawgit.com/w3c/wcag21/non-text-contrast-ac/understanding/21/non-text-contrast.html <https://rawgit.com/w3c/wcag21/non-text-contrast-ac/understanding/21/non-text-contrast.html%20%0d2>
2<https://rawgit.com/w3c/wcag21/non-text-contrast-ac/understanding/21/non-text-contrast.html%20%0d2>] https://rawgit.com/w3c/wcag21/non-text-contrast/understanding/21/non-text-contrast.html <https://rawgit.com/w3c/wcag21/non-text-contrast/understanding/21/non-text-contrast.html%20%0d3>
3<https://rawgit.com/w3c/wcag21/non-text-contrast/understanding/21/non-text-contrast.html%20%0d3>] https://www.w3.org/WAI/WCAG21/Understanding/use-of-color.html
Received on Saturday, 19 May 2018 23:03:25 UTC

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