For users with visual impairments or color blindness, color contrast is particularly important. Have a look at the two examples below:
Example 1: Low Contrast
Example 2: High Contrast
You can use an online tool, such as Contrast Checker, to ensure your page, font and button colors have an appropriate contrast. Note that the font size affects contrast, measuring at above and below 18pt fonts. You can also use this site to view how your site looks with greytones.
For those with color blindness, red and green, which are typical action button colors, are not recommended. Also check the contrast between button, hyperlink and menu colors and their hover colors, so that their hover state is clear.