Re: [csswg-drafts] [css-color] color-contrast() should support ranges of candidate colors, not just discrete color candidates (#7360)

Hi Bill @BillGoldstein 

>  _...some WCAG3 discussion of maximum contrasts..._

Yes, currently testing a maximum APCA contrast of what is currently calculated as Lc 90, this is on the live [SAPC development tool](https://www.myndex.com/SAPC/) along with a spread of use-case lookups.

There are a variety of factors that make a normative guideline for maximum contrast tricky:
- It is extremely polarity sensitive.
- KEY: It is LESS about a maximum _contrast_ and MORE about a maximum _luminance_ relative to adaptation state.
    - Since only estimated relative luminance can be determined, and there are privacy considerations for attempting to access the other needed parameters, this might be a showstopper, at least as a normative standard (i.e. only listed as an informative condition).
    - Since adaptation state is important, and the 3-way and 4-way APCA versions are considered future iterations (one step at a time, LOL) only local adaptation is directly considered, and that's not enough for predicting "max" contrast.
    - Newer HDR displays have modes viewing sRGB material that is eye-scorching, and then other modes marked "readable", and again, content authors have no control here. (See SAPC-APCA [discussion #74](https://github.com/Myndex/SAPC-APCA/discussions/74) for discussion of this exact use case).
- font weight and size are also key relevant factors, and for that matter so is age and related issues pertaining to ocular media, disability glare, etc.

So, at the moment, Lc 90 is an advisory maximum, especially in dark mode. But a better advisory MIGHT be, limit the color to no brighter than the equivalent of about ` #e6e6e6 `

A related advisory is for light mode, to keep the background under text to less than about ` #e6e6e6 ` as well.

Your mileage may vary, these values are under investigation.

Here's a visual example of some of the factors:


<img width="540" alt="New Eye Strain 2022" src="https://user-images.githubusercontent.com/42009457/174494439-43a1ee1f-b7cd-45c2-bd00-02fd00d29d8d.png">



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Received on Sunday, 19 June 2022 18:06:35 UTC