[css-mediaqueries] prefers-color-scheme and printing

[quasicomputational]

Spec: https://drafts.csswg.org/mediaqueries-5/#prefers-color-scheme (drive-by note: the section title is a copy-pasto)

What should the interaction of prefers-color-scheme and printing be? I'm specifically worried that 'prefers-color-scheme: dark' might naively cause printer ink worth more than the GDP of Hampshire to be used.

Some options off the top of my head, but I'm sure there are others:

• When printing, recommend (require?) that 'prefers-color-scheme: light' matches, because paper has a 'light' colour scheme. Is there such a thing as light-on-dark printing where this would be inappropriate?
• Have no preferred colour scheme when printing (a no-list of inappropriate media), or perhaps for all media except screens (a yes-list of appropriate media); queries involving prefers-color-scheme should always be false in those cases. This has a good forwards compatibility story if something else gets decided later.

[MatsPalmgren]

I think multiple UAs will soon ship this feature, so it would be good to have a decision on this.

[tabatkins]

Ultimately this is a UA matter; this MQ's resolution is based on how the UA chooses to represent the user's needs.

I feel like printing should prefer a light color scheme, regardless of what people prefer to look at on their screen. A note in that section saying so seems pretty reasonable?

[MatsPalmgren]

Seems reasonable to me.

[freund17]

I don't see the reason for having prefers-color-scheme behave differently, while in a printing context.
There already is @media print to detect, whether we are printing or not.
But the users color-preference did not change.

I understand the concern of wasting ink, but that has always been the case when developers/designers did not handle the print-case.

I have the feeling we are trying to be to clever here and making everything unnecessarily more complicated...

[css-meeting-bot]

The CSS Working Group just discussed prefers-color-scheme and printing, and agreed to the following:

• RESOLVED: Do not have any normative text about this. Add a note encouraging UAs to think about what should be done for printing and to use light when they know printing to paper

The full IRC log of that discussion

<dael> Topic: prefers-color-scheme and printing
<dael> github: https://github.com//issues/3522
<dael> emilio: Somebody asked if prefers color scheme should always be light web printing. Seems reasonableand I think it's what webkit does. BUt author can already check that. Should we define this?
<AmeliaBR> It sounds like something that the browser should include in their Print UI, just like turning off background images.
<AmeliaBR> (AKA, what Florian is saying)
<dael> florian: Feels like something up to UA. Seems reasonable UA choice to switch to light when prining. I think a checkbox in the print pop up is also reasonable as well. Saying UA can have a different preference sounds good, but forcing light is overkill
<dael> fantasai: I think suggest UA returns light when prining
<tantek> yes that seems reasonable
<dael> TabAtkins: What's returned is 100% UA determined, but most of the time you want light when printing. Have a note that this may vary on various factors, but printing should default to light
<dael> emilio: You might want dark if printing a PDF, but that's something the UA can expose. I'm happy to default to light
<emilio> s/emilio/dino
<dael> fantasai: Suggest if you expect to print to paper you should indicate a preference for white. Doesn't necessarily mean PDFs should default to light
<dael> astearns: Prop: Do not have any normative text about this. Add a note encouraging UAs to think about what should be done for printing and to use light when they know printing to paper
<dael> astearns: Objections?
<Rossen> unless the paper is black... :)
<dael> RESOLVED: Do not have any normative text about this. Add a note encouraging UAs to think about what should be done for printing and to use light when they know printing to paper

[grorg]

I'll update the spec.