What
Careful and intentional use of color is a cornerstone of accessible content creation. It is important not to use color alone to convey content – for example, using red text and nothing else to draw attention to keywords in lecture slides is inaccessible to some users. Special attention should be paid to use sufficient color contrast to ensure readability.
Why
Color contrast is necessary to provide access to users who cannot distinguish between certain colors and for people with low vision, but it also makes reading easier for everybody.