Visual Assistance

One large category of disability is visual impairment. This includes not just the blind, but those who are color blind or partially sighted, and require some additional consideration.

Color Contrast

When choosing colors for text or elements on a website, the contrast between them needs to be considered. For WCAG 2.0 AA, this means that the contrast ratio for text or visual representations of text needs to be at least 4.5:1.

There are tools online to measure the contrast ratio such as this color contrast checker from WebAIM or be checked with using automation tests.

Visual Information

Color can help a user's understanding of information, but it should never be the only way to convey information to a user. For example, a user with red/green color-blindness may have trouble discerning at a glance if an alert is informing them of success or failure.

Always be sure that color is not the only way information is being conveyed to the user.

Audiovisual Media

Audiovisual elements in the application such as video, sound effects or audio (ie. podcasts) need related textual representations such as transcripts, captions or descriptions. They also should never auto-play and playback controls should be provided to the user.

原文: https://angular-2-training-book.rangle.io/handout/a11y/key-concerns/visual-assistance.html