Accessibility requirements relevant to visual design generally cluster around issues of legibility, color perception and device independence.
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Accessible design is, at its heart, just "good" design: effective, highly usable visuals and interfaces to communicate with an audience. What is added is an awareness of certain limitations or needs of specific audience members.
Common design considerations for people with disabilities interacting with digital applications include:
- Users with low vision may struggle to read small text or discern differences between similar colors.
- Users with with distortions or artifacts in their visual field may struggle with designs which rely on distant spatial connections, such as form designs with a column of labels to the left of a column of fields.
- Users using magnification software will zoom in on individual pieces of the page. Alerts placed far from a cursor may appear off their screen, and scrollable in-page elements may prevent them from scrolling the page without zooming back out.
- Users with colorblindness and devices with "digital wellbeing" features that turn sepia/grayscale in the evening may not be able to differentiate color differences.
- Users with reading and attention disorders may struggle to read content if distractions pull their focus from the content or font choices increases their cognitive load.
Font and layout choices should make it easy for users to recognize characters and track lines. This is especially critical for users with low vision and cognitive disabilities relevant to reading or focus.
- The design should minimize distractions and make it easy for users to focus on the primary content.
- Ample space should separate grouped elements.
- Animations should be minimized or easily paused.
- Sans-serif fonts with line heights (leading) close to 1.5 and line lengths of less than 80 characters are usually easiest to read.
- Left aligned text maintains consistent character and word spacing. Inconsistently spaced words in justified text can make it difficult to read for some users, and the inconsistent left alignment of centered or right-aligned text is often mistaken for meaningful tab indentations.
- Very light weights (<300) of some fonts exhibit dramatically reduced contrast, blurriness and color shifts on some screens. Be sure to test light font weights on low and high PPI screens, on both Windows and Apple devices.
- Color contrast for text against its background should meet WCAG standards: 4.5:1 for small text, 3:1 for large text. Note that logos and disabled buttons are not held to these standards.
- Meaningful graphical elements (icons, focus indicators) should also maintain a 3:1 contrast against their background.
- Avoid using pure black (#000) against pure white (#FFF). Extreme contrast at a single pixel distance reduces legibility and increases eyestrain for many users, especially users with dyslexia and light sensitivity.
- When using more than one thematic color, try to use palettes which remain distinct for users with colorblindness.
- Avoid communicating concepts with color alone. Secondary indications such as icons, underlines or contrast changes may be needed to differentiate elements.
Suggested color selection and testing tools:
- Generate accessible palette suggestions with Color Safe, or the USWDS token based color system.
- Test simple color pairs in the WebAIM color checker and palettes using ColorCube or Contrast Grid.
- Color Contrast Analyser (CCA) provides an eyedropper to test on-screen colors in any application.
- Test all colors at once on existing sites using the "contrast" tab in WAVE. But note that WAVE cannot calculate colors for text on top of images or gradients; use CCA for this.
- Designs should be adaptable for many screen sizes:
- On small screens, elements should not become too small to see or overflow the screen horizontally.
- On large screens elements should not become blurry due to over-enlargement.
- The design should not require a particular orientation (vertical or horizontal).
- Designs should be adaptable for low and high pixel densities:
- Low PPI screens may need heavier weight fonts or simplified graphical elements.
- High PPI screens will need vector or high resolution images and logos.
- Text for links, buttons and menu items should clearly explain their purpose or destination.
- Visual indications that elements are interactive (links, buttons) should be clear and consistent, and should be reserved for interactive elements. Users should not have to figure out what they can click on through trial and error.
- Note that color changes alone would require a 3:1 contrast ratio with the non-interactive text, meaning it is often easier to rely on secondary indications (underlines, outlines, background colors).
- Maximize visual proximity for related elements and field labels.
- Make clicking and hovering forgiving of imprecision with amply sized touch targets, space between interactive elements, and forgiving mouse paths (e.g.: wide vertical dropdown paths remain open when a hovering mouse deviates a dozen pixels from a straight path; narrow horizontal flyouts would close).
- Navigational elements should appear in the same place and in the same order on each page, and indicate which page or section is active.
- A site search, content links, a site map or a similar alternate navigation should be available for users who do not find what they are looking for in the main menu.
- UX Foundations: Accessibility is a short, 80 minute class focused exclusively on design issues related to common disabilities and assistive devices, and is available through Princeton's LinkedIn Learning portal.
- Princeton's Safari Tech Subscription provides access to several recent books on accessibility in design and front-end development, including the excellent Accessibility for Everyone.
- Design-related accessibility articles appear frequently at A List Apart and Smashing Magazine.