[css-color-adjust] Opt-out mechanism from auto dark/forced dark for dark-by-design pages in `<meta name="color-scheme">`

[ananya-ky]

I have been reading through the recent issues around <meta name="color-scheme"> and the only keyword (#5089, #10249, #3881) and I had a couple of questions.

As I understand it, the possible values for the content attribute of the <meta> tag are-

• light - Document supports light; UA may still apply transformations (like forced dark)
• dark - Document supports dark; UA may still apply transformations.
• light dark/dark light - Document supports both; UA may choose based on the order, and user preference.
• only light- Document supports only light mode; no auto-darkening or forced dark mode will be applied.

However, only dark is valid in the color-scheme CSS property, but not valid in the <meta> tag as per MDN (see link below).

1. Is it truly the case as stated by MDN that only dark is invalid because it could force a document to render in a mode for which it is not designed?

   Since the author of the document requested only dark, can't we assume that they understand whether their document is compatible with dark mode?

   The Color Adjustment spec does not explicitly say only dark is invalid. Is it the case that the spec and MDN disagree on the validity of only dark?

2. How can we tell the UA to not apply transformations like auto darkening/forced darkening for a page that is dark by design?

   The reason I ask this is because there are situations where color reproduction remains critical. A page that looks dark may still want to ensure that the UA doesn't modify the colours.

   • It seems counter-intuitive to ask authors of a page that looks dark to use only light to indicate this.. In terms of UX, the user may need to activate 'light' mode to get the page to look dark in the way they expect.

   • We understand that there are likely few pages that are designed exclusively for dark mode (and that would require UA to render widgets in dark mode - something not all UAs are capable of doing). In many cases, authors style these components themselves, rather than relying on UA-provided theming for the widgets. Was this the reason behind the decision not to support only dark, if it is indeed invalid?

[lukewarlow]

To answer question 2: Simply put color-scheme dark, that way browsers won't try to auto darken the page.

For question 1, I would be very surprised if MDN was actually correct here. dark vs dark only should have no impact, there's not auto lightening user agent and so they should just be equivalent. That being said dark only shouldn't be invalid, merely not that useful.