Safari 27.3 beta can darken light websites on its own, and the sites cannot detect it

Safari 27.3 beta adds Adaptive Dark Mode, a setting that shows light websites in dark colors when they have no dark theme of their own, WebKit announced on November 3, 2026. The change matters to anyone who runs a site: a visitor who turns it on can see a page in colors its authors never chose, and the page has no way to find out.

What the visitor sees

The mode is opt-in. With the system appearance set to dark, a visitor who opens a site with a bright background gets a preview from Safari and accepts it by tapping Try.

WebKit presents the feature as an answer to a measured gap. According to the team's figures, almost 40% of web page loads come from users in dark mode, while only 10% of page loads support it.

How the page changes

Safari first looks for a signal from the site. A page that declares color-scheme: light dark in CSS, or <meta name="color-scheme" content="light dark"> in HTML, stays as it is. For the rest, Safari estimates whether the page is mostly light or mostly dark and changes only the light ones.

The core of the feature is a color matrix that inverts a color's luminosity, meaning how light or dark it is, while keeping its hue. Light backgrounds become dark and dark text becomes light. For text, the target is the 4.5:1 contrast ratio from WCAG, the web accessibility guidelines.

Images and effects are handled separately:

• Most images stay unchanged.
• SVG images are inspected and recolored when needed.
• Bitmap images are analyzed by pixel histogram, and simple black-and-white logos are inverted.
• Content in a <canvas> element is left unchanged.
• Effects such as masks and mix-blend-mode can be switched off on a recolored element.

What site owners can do

A site that wants full control can build its own dark theme and declare it, and Safari then changes nothing. WebKit recommends declaring color-scheme in the HTML head or on :root or body in CSS, rather than injecting it later with JavaScript.

A site can also refuse the transformation with color-scheme: light only or the matching meta tag. WebKit notes that Safari 27.3 beta 1 does not yet support the only keyword, so that refusal cannot be tested in this build.

Pages that stay light benefit from smaller fixes: SVG logos instead of bitmaps, CSS colors instead of tiled background images, modern CSS instead of image sprites, and images with transparent backgrounds.

Why a site cannot tell

WebKit says this protects privacy. A detectable setting would give trackers one more signal for fingerprinting, the practice of recognizing a browser by its combination of traits. JavaScript that reads CSS colors therefore gets the authored values rather than the ones on screen, and images drawn into a <canvas> render in their original form.

The post gives no date for a stable release.