See Understanding Techniques. Situation A: text is less than 18 point if not bold and less than 14 point if bold G17: Ensuring that a contrast ratio of at least 7:1 exists between text (and images of text) and background behind the text G148: Not specifying background color, not specifying text color, and not using technology features that change those defaults G174: Providing a control with a sufficient contrast ratio that allows users to switch to a presentation that uses sufficient contrast Situation B: text is as least 18 point if not bold and at least 14 point if bold G18: Ensuring that a contrast ratio of at least 4.5:1 exists between text (and images of text) and background behind the text G148: Not specifying background color, not specifying text color, and not using technology features that change those defaults G174: Providing a control with a sufficient contrast ratio that allows users to switch to a presentation that uses sufficient contrast Advisory Techniques for Success Criterion 1.4.6 G156: Using a technology that has commonly-available user agents that can change the foreground and background of blocks of text Failures for Success Criterion 1.4.6 F24: Failure of Success Criterion 1.4.3, 1.4.6 and 1.4.8 due to specifying foreground colors without specifying background colors or 
 vice versa F83: Failure of Success Criterion 1.4.3 and 1.4.6 due to using background images that do not provide sufficient contrast with foreground text (or images of text) Back to top 1.4.7 Low or No Background Audio Level AAA For prerecorded audio-only content that (1) contains primarily speech in the foreground, (2) is not an audio CAPTCHA or audio logo, and (3) is not vocalization intended to be primarily musical expression such as singing or rapping, at least one of the following is true: No Background: The audio does not contain background sounds. Turn Off: The background sounds can be turned off. 20 dB: The background sounds are at least 20 decibels lower than the foreground speech content, with the exception of occasional sounds that last for only one or two seconds. Per the definition of "decibel," background sound that meets this requirement will be approximately four times quieter than the foreground speech content.