The color of the text and the color of the background must have sufficient contrast to each other to be accessible. Insufficient contrast between text and its background can give problems for users with visual impairments and color blindness, but it can also affect a lot of other users, leading to important text potentially being overlooked.
The contrast ratio should be at least 4.5:1 for normal text and 3:1 for large text.
Fixing color contrast issues
Use dev tools in SiteImprove to locate errors
Use color contrast tools such as www.0to255.com
Lea Verou's WCAG 2.0 color contrast tool helps web developers decide what color combinations provide enough contrast to meet the WCAG 2.0 guidelines
Colour Contrast Check is a useful tool for checking the degree of contrast between foreground and background colors you might be using