The human eye is subjective,
and variables like monitor quality and lighting conditions are completely unpredictable.
There are, however, some general rules of thumb. Avoid red text??”or equally
dark colors??”on black backgrounds. Avoid very light grays or light blues on white backgrounds.
Avoid tonally neutral backgrounds, like medium gray, which can wash out the
contrast of any colored text.
From a technical standpoint, the magic ratio for everyday contrast is 5:1. The Web
Accessibility Tools Consortium12 has produced a very useful tool called the Colour Contrast
Analyser, which measures two colors and reports back the contrast ratio. For instance,
dark red (#800000) text on a black background (#000000) produces a measly ratio of
1.93:1, completely inadequate for reading. Compare that to white text (#FFFFFF) on a field
of dark blue (#000080), and the ratio jumps to 15.95:1, a highly legible contrast.
ACCESSIBILITY
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12. www.wat-c.org/tools/CCA/1.1
Most sites have good contrast for normal viewing, but for some, good color
choices are simply not enough. Visually impaired visitors need high-contrast
versions of your site, the equivalent of large-type books.
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