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An important aspect of color for both low vision and colorblind users is sufficient contrast between the background and foreground (text or graphics). Color schemes can be changed in most documents, but it is most commonly a factor in PowerPoint, HTML Web pages and Flash.

Below are some general recommendations with some references to PowerPoint.

Contrast Just Right

The maximum contrast is black vs. white but other options are available such as navy/white, cream/dark brown, yellow/black and similar color schemes. Generally speaking, a color scheme is considered legible if it can be read in grayscale/black and white mode.

For a more specific information and tests, read the Contrast for the Web page.

Colors to Avoid

Orange

Orange should ONLY be used with large text and as a highlight. Because orange is neither very dark or very light, it is difficut to contrast it with another color.

Red vs. Green

This particular combination can be problematic because many color deficient viewers cannot distinguish these two colors. They are also both about the same level of darkness which is problematic for contrast.

Too Vivid

Large blocks of brightly colored text should be avoided. Adjacent areas of bright colors can cause issues with both visual vibration and, ironically, value contast.

Instead use colors like red, royal blue and emerald green for decorative blocks, large headlines, highlighting words or for links. See the Working with Bright Colors page for more details.

Too Much Texture

A slide or background with a texture (including a gradient) can also interfere with legibility. The more subtle the background, the more likely it is that the text will be legible. See the Color and Background Texture page for some examples of good and bad textures.

Too Subtle

The examples above are generally cases of a color scheme being "too garish," but it is also possible to be "too tasteful." Some modern color schemes feature such subtle contrasts, it can actually be insufficient for some readers.

Examples include contrasting light grey versus middle grey, middle pastels versus darks, or white versus light cyan (blue-green).
If you plan to use a subtle color palette, again make sure that a black and white printout can be read.

Overly Subtle Color Schemes

Color Scheme	Too Little Contrast	Sufficient Contrast
gray/white	gray on white	gray on white
dark gray/light gray	light gray on dark gray	light gray on dark gray
teal/white	teal on white	teal on white
sea green/green	sea green on green	sea green on green
orange/white	orange on white	red-orange on white
red/white	red on white	crimson on white
links on black	mid blue on black	lighter blue on black

WCAG 2.0 Guidelines

A detailed discussion of exact luminosity ratios required and how to test on Web pages can be found on Contrast for Web Pages.

Beware Color Coding

Using color coding alone to convey information can also be problematic for blind and color deficient users (particularly those who cannot distinguish red vs. green). Color coding should always be supplemented with some other mechanism such as a shape or symbol. See the Color Coding page for suggestions.

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