Adhering to WCAG 2.0 criteria for color contrast can be important for many organizations to meet the needs of their users. The following articles and websites are resources for understanding ADA guidelines regarding colors.
Understanding Color Contrast
The World Wide Web Consortium has detailed extensively the guidelines for color contrast on the web with examples.
This is an excellent resource for assembling compliant color palettes to be used to style your map
Wave Accessibility Checker
After applying compliant styles to your map, test that it passes contrast tests using this tool from WebAIM