Color contrast: When this check fails, it’s possible that the document contains content that is not accessible to people who have low vision or color deficiencies.
To fix this issue, make sure that the document’s content adheres to the guidelines outlined in WCAG section 1.4.3 or include a recommendation that the PDF viewer use high-contrast colors and verify that all content is readable in the high-contrast color scheme.
To check the document in a high contrast color scheme perform the following:
Choose Edit > Preferences (Windows) or Acrobat > Preferences (Mac OS).
Choose the Accessibility category.
Select Replace Document Colors, and then select Use High-Contrast Colors. Choose the color combination that you want from the pop-up menu, and then click OK (See “Figure 9. Adjust Viewer to Display Document with High Contrast Settings”).