Page Content
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.
| 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.