High-contrast color schemes are easier to read because the text is more pronounced against the background, making it ideal for visually impaired visitors.
The World Wide Web Consortium's (W3C's) Web Content Accessibility Guidelines (WCAG) 2.0 says websites should feature a color contrast ratio of at least 4.5-to-1 for regular text or 3-to-1 for headings. To put those figures into perspective, a black-and-white color scheme offers the highest color contrast ratio at 21-to-1, whereas using two of the same colors offers the lowest color contrast ratio at 1-to-1.
To choose a high-contrast color scheme, play around with the free tool at colorsafe.co. On the right-hand side of the tool, you can select from either the "AA" or "AAA" WCAG standard. The AA standard is the minimum color contrast ratio required for WCAG compliance, making it less restrictive than the AAA standard. Choosing the AAA standard, however, will reveal color combinations with a higher contrast ratio, which is ideal when optimizing your website for visually impaired visitors.