It is an error not to specify a background color when

It is an error not to specify a background color when specifying text color because the default background color set by users is unknown and cannot be tested for sufficient contrast. Note 3: For the purposes of success criteria 1.4.3 and 1.4.6, contrast is measured against a specific background on which text is displayed under normal operating conditions. It is also more difficult to change the contrast and color combinations of foreground and background text images, which is necessary for some users. Therefore, in this recommendation, contrast is calculated so that color is not a determining factor, so that people with color vision impairments can get the appropriate contrast between text and background. Text with 18 paragraphs or bold text with 14 paragraphs is considered large enough to require a lower contrast ratio. Note: Some people with cognitive disabilities require low contrast color schemes or shades. Therefore, we allow and encourage authors to provide mechanisms for adjusting the foreground and background colors of content. Note 4: The background color is the specified color of the content over which the text should appear in normal use. The 3:1 contrast ratio is the minimum recommended by [ISO-9241-3] and [ANSI-HFES-100-1988] for standard text and images. When creating images containing large amounts of text, authors should ensure that the resulting image text is approximately 1.2 and 1.5 inches or 120% and 150% of the size of the standard main text displayed by the browser.