Who Can Use - WhoCanUse is a tool that brings attention and understanding to how color contrast can affect different people with visual impairments.
Colour Contrast Analyser - TPGi's ADA Color Contrast Checker checks for helps determine the accessibility the contrast ratio of two colors for WCAG AA and AAA.
Palette For Mac - A menu bar based colour contrast analyser
Kontrast - Check and adjust web element contrast in real time.
Koa11y - Automatically detect accessibility (a11y) issues on webpages
Colordot for iOS - A color picker for humans.