Increased contrast

Somebody has already decided, in system settings, that your defaults are too soft. Apple platforms call it Increase Contrast, Android has a high contrast text setting, Windows ships contrast themes, and the browser passes the request on as prefers-contrast, whose values are more, less, custom, and no-preference. The reasons are ordinary: low vision, ageing eyes, glare on a phone outdoors, a cheap monitor at a bad angle. Most of the people it helps have never opened an accessibility menu in their lives; they just turned it on because things were hard to read.

Honouring it is mostly about restoring edges that a modern theme spent years removing. Hairline dividers go to full ink, ghost buttons get a real border, secondary text stops being three shades down, placeholder and helper text come up, focus indicators thicken, and states that were carried by a faint tint get an outline or a shape as well. What it is not is a saturation crank. Pushing hue and chroma around usually makes text harder to read, not easier, and it breaks the palette’s meaning at the same time. Strengthen lightness differences and let the hues stay where they are.

prefers-contrast is a request, and forced-colors is an override. When a Windows contrast theme is active, forced-colors: active matches and the browser substitutes the user’s own palette for most of your colours whether you asked for it or not. The job then changes: stop painting, start checking. Use the system colour keywords (Canvas, CanvasText, LinkText, ButtonFace), make sure anything you drew with background images or box shadows still exists when they are dropped, and reach for forced-color-adjust: none only for the rare element whose colours carry information no substitute can express.

The preference never buys you out of the baseline. WCAG’s contrast minimums apply to the default theme, and a design that only becomes readable once the reader finds a setting has failed the people who never find it. Treat the increased-contrast rendering as a stronger version of a design that already passed, not as the version where the numbers finally work.