Making 1.4.1 use of color info on state requirements for 1.4.11 into new sufficient and failure techniques

[mbgower]

After discussion on 1.4.11 Non-Text Contrast and use of color for state indicators, the current information on use of color and relative luminence will be removed and a new success technique and failure technice, similar to https://www.w3.org/TR/WCAG20-TECHS/G183 and https://www.w3.org/TR/WCAG20-TECHS/F73.

The current text being removed from the exisiting Understanding document wording is:

Note on SC 1.4.1 Use of Color

1.4.1 states "Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element." Although every object on a screen is arguably created through use of color only (shapes are created by altering a bunch of pixels from white to another color), the context made clear in the Understanding document is that 1.4.1 addresses changing only the color of an object (or text) without otherwise altering the object's form. If an author adds an outline or shadow to a shape to indicate a change in state, that is not relying solely on use of color. Relative luminence: If the selected and unselected states of an object do vary only by color, this is still acceptable so long as the luminosity contrast ratio between the selected and unselected colors differs by at least 3:1. User agent enhancment: If the author-supplied visual indicators of change in state vary only by color, this is still acceptable if the user agent provides a redundant visual effect which authors do not obscure.

[alastc]

The cross-reference text is in this commit and should be preview-able on the working branch.

[michael-n-cooper]

This issue was moved to w3c/wcag#402