Many users will have visual impediments that will require good contrast in the documents you are producing. The best way to help these users is to make sure that the contrast between background and foreground has a ratio of 4.5:1 or higher. Leaving the defaults of the editor intact is best - black text on white, with a ratio of 21:1.

Everybody experiences the world, including content they access on the internet, in their own way.  How someone experiences content on the internet can be vastly different depending on the computer or device and size of the screen on which they view it, and how they interact with it.

For example, while some people read text and interpret images they view, others use assistive technology to listen to content using a screen reader.  Meanwhile, some people click on links using a mouse or similar device, while others navigate using a keyboard or by tapping on touch screens.

Improving the accessibility of content is about reducing basic barriers to comprehension, such as providing alternative text for images, so that those who cannot see the images can grasp their meaning.  Similarly, making captions or transcript text available for a video file can make it accessible to someone who cannot hear audio.

For more technical information about making content accessible, see What are some guidelines for making content accessible?