CSS Color Adjustment Module Level 1

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Elika J. Etemad / fantasai (Invited Expert)
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This module introduces a model and controls over automatic color adjustment by the user agent to handle user preferences, such as "Dark Mode", contrast adjustment, or specific desired color schemes.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, etc.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This document was published by the CSS Working Group as a Working Draft. Publication as a Working Draft does not imply endorsement by the W3C Membership.

This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

Please send feedback by filing issues in GitHub (preferred), including the spec code “css-color-adjust” in the title, like this: “[css-color-adjust] …summary of comment…”. All issues and comments are archived. Alternately, feedback can be sent to the (archived) public mailing list www-style@w3.org.

This document is governed by the 15 September 2020 W3C Process Document.

This document was produced by a group operating under the W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

1. Introduction

1.1. Value Definitions

This specification follows the CSS property definition conventions from [CSS2] using the value definition syntax from [CSS-VALUES-3]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. Combination with other CSS modules may expand the definitions of these value types.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the CSS-wide keywords as their property value. For readability they have not been repeated explicitly.

2. Preferred Color Schemes

Operating systems and user agents often give users the ability to choose their preferred color schemes for user interface elements. These are typically reflected in the user agent’s rendering of its navigation interface as well as in-page interface elements such as form controls and scrollbars, and are expected to also be reflected in the values of the CSS system colors.

A UA can also allow the user to indicate a preference for the color scheme of the pages they view, requesting that the author adapt the page to those color preferences. (It is not required to express a preference; users can have preferences for operating system interface colors that they do not want imposed on pages.)

The most common preferences are a choice of “Light” vs “Dark” (or “Day Mode” vs “Night Mode”) color schemes, rendering things as mostly light- or dark-colored backgrounds, and with dark- or light-colored foregrounds (text, icons). This module, together with Media Queries Level 5, defines controls to enable color scheme negotiation for “Light” and “Dark” color schemes (and no preference).

Note: The “Light” and “Dark” color schemes don’t represent an exact color palette (such as black-and-white), but a range of possible palettes. To guarantee specific colors, authors must specify those colors themselves. Note also that, consequently, pairing default or <system-color> colors with author-specified colors cannot guarantee any particular contrast level; it might be necessary to set both foreground and background colors together to ensure legibility [WCAG21].

To enable pages to adapt to the user’s preferred color scheme, user agents will match the prefers-color-scheme media query to the user’s preferred color schemes. See [MEDIAQUERIES-5].

Additionally, if the author has indicated that the page can support this color scheme (see color-scheme), the user agent must match the following to the user’s preferred color scheme:

User agents may support additional color schemes, however CSS does not support negotiation of additional color schemes: user agents should pursue standardization of these schemes, so that prefers-color-scheme and color-scheme can reflect the additional values.

Note: Aside from the small list of adjustments given above, user agents generally do not further adjust a page to match the user’s preferred color scheme, because the chance of accidentally ruining a page is too high. However, when particular color choices are required by the user (for accessibility reasons, for example), more invasive changes might be applied; see § 3 Forced Color Schemes.

2.1. Opting Into a Preferred Color Scheme: the color-scheme property

Name: color-scheme
Value: normal | [ light | dark | <custom-ident> ]+
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: the keyword normal, or an ordered list of specified color scheme keywords
Canonical order: per grammar
Animation type: discrete

The color-scheme property allows an element to indicate which color schemes it is comfortable being rendered with. These values are negotiated with the user’s preferences, resulting in a used color scheme that affects UI things such as the default colors of form controls and scrollbars as well as the used values of the CSS system colors.

Values are defined as follows:


Indicates that the element isn’t aware of color schemes at all, and so the element should be rendered with the browser’s default color scheme.

[ light | dark | <custom-ident> ]+

Indicates that the element is okay with being rendered with any of the listed color schemes.

If the user’s preferred color scheme, as indicated by the prefers-color-scheme media feature, is present among the listed color schemes, and is supported by the user agent, that’s the element’s used color scheme.

Otherwise, if the user agent supports at least one of the listed color schemes, the used color scheme is the first supported color scheme in the list.

Otherwise, the used color scheme is the browser default. (Same as normal.)

light represents a “light” color scheme, with light background colors and dark foreground colors. dark represents the opposite, with dark background colors and light foreground colors.

Note: User agents are not required to support any particular color scheme, so only using a single keyword, such as color-scheme: dark, to indicate a required color scheme is still not guaranteed to have any effect on the rendering of the element.

<custom-ident> values are meaningless, and exist only for future compatibility, so that future added color schemes do not invalidate the color-scheme declaration in legacy user agents. User agents must not interpret any <custom-ident> values as having a meaning; any additional recognized color schemes must be explicitly added to this property’s grammar. To avoid confusion, authoring tutorials and references should omit <custom-ident> from their materials.

normal, light, and dark are not valid <custom-ident>s in this property.

Note: Repeating a keyword, such as color-scheme: light light, is valid but has no additional effect beyond what the first instance of the keyword provides.

A well-written page—one that responds to user preferences for light or dark display by using the prefers-color-scheme media feature to alter the colors it uses—can easily opt the browser-controlled UI (scrollbars, inputs, etc) into the user’s preferred color scheme as well with a simple global declaration:
:root {
  color-scheme: light dark;
If a page limits itself to using only the <system-color>s, it can support the user’s preferred color scheme without needing to use @media at all, simply by using the color-scheme property:
:root {
  color-scheme: light dark;

because the used color scheme affects what <system-color>s resolve to.

Note: “Light” and “dark” color schemes are not specific color palettes. For example, both a stark black-on-white scheme and a sepia dark-on-tan scheme would both be considered “Light” color schemes. To ensure particular foreground or background colors, they need to be specified explicitly.

Note: [HTML] specifies a color-scheme meta tag which can be used to set the color-scheme on the root element as a non-CSS presentational hint.

Note: Earlier versions of this property also defined an only keyword to be specified alongside a preferred color scheme, indicating a stronger author preference. It ended up being unnecessary, and was removed.

2.2. Effects of the Used Color Scheme

For all elements, rendering with a color scheme should cause the colors used in all browser-provided UI for the element—e.g. scrollbars, spellcheck underlines, form controls, etc.—to match with the intent of the color scheme.

On the root element, rendering with a color scheme additionally must affect the surface color of the canvas, the initial value of the color property, and the used values of the system colors, and should also affect the viewport’s scrollbars.

In order to preserve expected color contrasts, in the case of embedded documents typically rendered over a transparent canvas (such as provided via an HTML iframe element), if the used color-scheme of the element and the used color-scheme of the embedded document’s root element do not match, then the UA must use an opaque canvas of the Canvas color appropriate to the embedded document’s color-scheme instead of a transparent canvas. This rule does not apply to documents embedded via elements intended for graphics (such as img elements embedding an SVG document).

3. Forced Color Schemes

Forced colors mode is an accessibility feature intended to increase the readability of text through color contrast. Individuals with limited vision often find it more comfortable to read content when there is a a particular type of contrast between foreground and background colors.

Operating systems can provide built-in color themes, such as Windows’ high contrast black-on-white and high-contrast white-on-black themes. Users can also customize their own themes, for example to provide low contrast or hue contrast.

In forced colors mode, the user agent enforces the user’s preferred color palette on the page, overriding the author’s chosen colors for specific properties, see § 3.1 Properties Affected by Forced Colors Mode. It may also enforce a “backplate” underneath text (similar to the way backgrounds are painted on the ::selection pseudo-element) to ensure adequate contrast for readability.

To enable pages to adapt to forced colors mode user agents will match the forced-colors media query and must provide the required color palette through the CSS system colors (see [CSS-COLOR-4]). Additionally, if the UA determines, based on Lab lightness, that the Canvas color is clearly either dark (L < 33%) or light (L > 67%), then it must match the appropriate value of the prefers-color-scheme media query and express a corresponding user preference for color-scheme. This will allow pages that support light/dark color schemes to automatically adjust to more closely match the forced color scheme. Behavior between the above dark vs. light thresholds is UA-defined, and may result in assuming either light or dark as the user’s preferred color scheme.

3.1. Properties Affected by Forced Colors Mode

When forced colors mode is active and forced-color-adjust is auto (see below) on an element, colors on the element are force-adjusted to the user’s preferred color palette.

Specifically, for each of the following properties:

if its computed value is a color other than a system color, its used value is forced to a system color as follows:


UAs may further tweak these forced colors mode heuristics to provide better user experience.

3.2. Opting Out of a Forced Color Scheme: the forced-color-adjust property

Name: forced-color-adjust
Value: auto | none
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Canonical order: per grammar
Animatable: not animatable

The forced-color-adjust property allows authors to opt particular elements out of forced colors mode, restoring full control over the colors to CSS. Values have the following meanings:


The element’s colors are automatically adjusted by the UA in forced colors mode.


The element’s colors are not automatically adjusted by the UA in forced colors mode.

Authors should only use this value when they are themselves adjusting the colors to support the user’s color and contrast needs and need to make changes to the UA’s default adjustments to provide a more appropriate user experience for those elements.

Should this property be merged with color-adjust somehow?

In order to not break SVG content, UAs are expected to add the following rules to their UA style sheet:

@namespace "http://www.w3.org/2000/svg";
svg|svg { forced-color-adjust: none; }
svg|foreignObject { forced-color-adjust: auto; }

4. Performance-based Color Schemes: the color-adjust property

On most monitors, the color choices that authors make have no significant difference in terms of how the device performs; displaying a document with a white background or a black background is approximately equally easy.

However, some devices have limitations and other qualities that make this assumption untrue. For example, printers tend to print on white paper; a document with a white background thus has to spend no ink on drawing that background, while a document with a black background will have to expend a large amount of ink filling in the background color. This tends to look fairly bad, and sometimes has deleterious physical effects on the paper, not to mention the vastly increased printing cost from expending the extra ink. Even fairly small differences, such as coloring text black versus dark gray, can be quite different when printing, as it switches from using a single black ink to a mixture of cyan, magenta, and yellow ink, resulting in higher ink usage and lower resolution.

As a result, in some circumstances user agents will alter the styles an author specifies in some particular context, adjusting them to be more appropriate for the output device and to accommodate what they assume the user would prefer. However, in some cases the document may be using colors in important, well-thought-out ways that the user would appreciate, and so the document would like some way to hint to the user agent that it might want to respect the page’s color choices. The color-adjust property controls this.

Name: color-adjust
Value: economy | exact
Initial: economy
Applies to: all elements
Inherited: yes
Percentages: N/A
Computed value: specified keyword
Canonical order: per grammar
Animation type: discrete

The color-adjust property provides a hint to the user-agent about how it should treat color and style choices that might be expensive or generally unwise on a given device, such as using light text on a dark background in a printed document. If user agents allow users to control this aspect of the document’s display, the user preference must be respected more strongly than the hint provided by color-adjust. It has the following values:

The user agent should make adjustments to the page’s styling as it deems necessary and prudent for the output device.

For example, if the document is being printed, a user agent might ignore any backgrounds and adjust text color to be sufficiently dark, to minimize ink usage.

This value indicates that the page is using color and styling on the specified element in a way which is important and significant, and which should not be tweaked or changed except at the user’s request.

For example, a mapping website offering printed directions might "zebra-stripe" the steps in the directions, alternating between white and light gray backgrounds. Losing this zebra-striping and having a pure-white background would make the directions harder to read with a quick glance when distracted in a car.

5. Privacy and Security Considerations

Applying user color preferences via color schemes or forced colors mode exposes the user’s color preferences to the page via getComputedStyle(), which can increase fingerprinting surface.

Additionally, it may be possible for an embedded document to use timing attacks to determine whether its own color-scheme matches that of its embedding iframe or not.

6. Acknowledgements

This specification would not be possible without the development efforts of various color adjustment features at Apple, Google, and Microsoft as well as discussions about print adjustments on www-style. In particular, the CSS Working Group would like to thank: Alison Maher, François Remy, イアンフェッティ

List additional MSFT / Apple / Google people here.

7. Changes

Changes since the 23 May 2019 Working Draft:


Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

Partial implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

Implementations of Unstable and Proprietary Features

To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

Non-experimental implementations

Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at https://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

CR exit criteria

For this specification to be advanced to Proposed Recommendation, there must be at least two independent, interoperable implementations of each feature. Each feature may be implemented by a different set of products, there is no requirement that all features be implemented by a single product. For the purposes of this criterion, we define the following terms:

each implementation must be developed by a different party and cannot share, reuse, or derive from code used by another qualifying implementation. Sections of code that have no bearing on the implementation of this specification are exempt from this requirement.
passing the respective test case(s) in the official CSS test suite, or, if the implementation is not a Web browser, an equivalent test. Every relevant test in the test suite should have an equivalent test created if such a user agent (UA) is to be used to claim interoperability. In addition if such a UA is to be used to claim interoperability, then there must one or more additional UAs which can also pass those equivalent tests in the same way for the purpose of interoperability. The equivalent tests must be made publicly available for the purposes of peer review.
a user agent which:
  1. implements the specification.
  2. is available to the general public. The implementation may be a shipping product or other publicly available version (i.e., beta version, preview release, or "nightly build"). Non-shipping product releases must have implemented the feature(s) for a period of at least one month in order to demonstrate stability.
  3. is not experimental (i.e., a version specifically designed to pass the test suite and is not intended for normal usage going forward).

The specification will remain Candidate Recommendation for at least six months.


Terms defined by this specification

Terms defined by reference


Normative References

Bert Bos; Elika Etemad; Brad Kemper. CSS Backgrounds and Borders Module Level 3. 17 October 2017. CR. URL: https://www.w3.org/TR/css-backgrounds-3/
Elika Etemad; Tab Atkins Jr.. CSS Cascading and Inheritance Level 4. 18 August 2020. WD. URL: https://www.w3.org/TR/css-cascade-4/
Tab Atkins Jr.; Chris Lilley. CSS Color Module Level 4. 5 November 2019. WD. URL: https://www.w3.org/TR/css-color-4/
Håkon Wium Lie; Florian Rivoal; Rachel Andrew. CSS Multi-column Layout Module Level 1. 15 October 2019. WD. URL: https://www.w3.org/TR/css-multicol-1/
Daniel Glazman; Elika Etemad; Alan Stearns. CSS Pseudo-Elements Module Level 4. 25 February 2019. WD. URL: https://www.w3.org/TR/css-pseudo-4/
Tantek Çelik; Rossen Atanassov. CSS Scrollbars Module Level 1. 25 September 2018. WD. URL: https://www.w3.org/TR/css-scrollbars-1/
Elika Etemad; Koji Ishii. CSS Text Decoration Module Level 3. 13 August 2019. CR. URL: https://www.w3.org/TR/css-text-decor-3/
Tantek Çelik; Florian Rivoal. CSS Basic User Interface Module Level 3 (CSS3 UI). 21 June 2018. REC. URL: https://www.w3.org/TR/css-ui-3/
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 3. 6 June 2019. CR. URL: https://www.w3.org/TR/css-values-3/
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 4. 31 January 2019. WD. URL: https://www.w3.org/TR/css-values-4/
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. REC. URL: https://www.w3.org/TR/CSS2/
Simon Pieters; Glenn Adams. CSS Object Model (CSSOM). 17 March 2016. WD. URL: https://www.w3.org/TR/cssom-1/
Elika Etemad; Tab Atkins Jr.. CSS Fill and Stroke Module Level 3. 13 April 2017. WD. URL: https://www.w3.org/TR/fill-stroke-3/
Anne van Kesteren; et al. HTML Standard. Living Standard. URL: https://html.spec.whatwg.org/multipage/
Dean Jackson; Florian Rivoal; Tab Atkins Jr.. Media Queries Level 5. 31 July 2020. WD. URL: https://www.w3.org/TR/mediaqueries-5/
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119

Informative References

Chris Lilley; et al. CSS Color Module Level 5. 3 March 2020. WD. URL: https://www.w3.org/TR/css-color-5/
CSS Conditional Rules Module Level 3 URL: https://www.w3.org/TR/css3-conditional/
Andrew Kirkpatrick; et al. Web Content Accessibility Guidelines (WCAG) 2.1. 5 June 2018. REC. URL: https://www.w3.org/TR/WCAG21/

Property Index

Name Value Initial Applies to Inh. %ages Ani­mat­able Anim­ation type Canonical order Com­puted value
color-adjust economy | exact economy all elements yes N/A discrete per grammar specified keyword
color-scheme normal | [ light | dark | <custom-ident> ]+ normal all elements yes n/a discrete per grammar the keyword normal, or an ordered list of specified color scheme keywords
forced-color-adjust auto | none auto all elements yes n/a not animatable per grammar as specified

Issues Index

find what we name this in other specs
Should this property be merged with color-adjust somehow?
List additional MSFT / Apple / Google people here.