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.
The image above contains examples of text with varying contrast ratios, and indicates whether the level of contrast would be adequate.
In most cases the contrast will be obvious, but if you need to verify, take the following steps: