Good color contrast is an important aspect of accessibility. It’s important to provide good contrast between text and the background. These tools can help you determine if the colors you have chosen provide adequate contrast.
Joe Dolson’s Color Contrast Tester: This tool includes Hex, RGB and HSL inputs.
WebAIM’s Color Contrast Checker: This is for Hex values only. The page includes some other resources and information that is helpful.
contrastchecker.com: This tool allows for Hex and RGB inputs. It also includes a color picker and the option to upload an image.