Leave text colors default, or set both
There is a way to pass contrast without measuring anything. G148 says specify no text color, specify no background color, and use nothing that overrides those defaults. The browser then decides both, and whatever the reader has configured simply works. W3C lists it as sufficient at three rules. Contrast at Level AA, plus the enhanced contrast and visual presentation rules at Level AAA. That reach follows from one fact. A page specifying no colors cannot fail a color threshold. The danger is the half-measure, and W3C's own title for the technique spells it out. Setting text color while leaving the background to the browser is a bet that every visitor's default is the one you had in mind. For anyone running a dark or high-contrast scheme, that bet produces text the same color as its background.
How we find it in an audit
A scan can tell us where a color is declared with no partner. That is the exact pattern this technique warns about. Our reviewers then load the site under a dark scheme and a forced-colors mode, looking for text that vanishes. Half-declared colors survive testing on a white default and disappear the moment somebody changes theirs.
How affected users experience it
People who have set their own colors have usually done it because the default is unreadable for them, so the settings are not a preference to override. Light sensitivity, low vision and some cognitive conditions all lead people there. When a site declares one half of the pair, their careful setup collides with the author's guess, and the result is invisible text with no error and no explanation.
Passes vs. fails
Passes
The site either declares text and background together at 4.5:1 or better, or declares neither and inherits the reader's own defaults.
Fails
The stylesheet sets color: #333 on body text and never sets a background, gambling that every visitor's default is white.
How this gets tested
The W3C publishes test rules that define what a checker looks for here.
- Text has enhanced contrastA tool can check this
- Text has minimum contrastA tool can check this
Other ways to satisfy this rule
7 guides on this site are filed under 1.4.3 Contrast (Minimum). W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
- G18sufficientMeet the 4.5:1 contrast ratio for text
- G145sufficientGive large text at least 3:1 contrast
- G174sufficientOffer a working switch to high-contrast view
- G156advisoryKeep text recolorable by the user's browser
- F24failureNever set text color without its background
- F83failureDo not set text over a low-contrast background image
This guide is our interpretation of W3C technique G148: Not specifying background color, not specifying text color, and not using technology features that change those defaults. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.