Who Can Use - WhoCanUse is a tool that brings attention and understanding to how color contrast can affect different people with visual impairments.
Palette For Mac - A menu bar based colour contrast analyser
Kontrast - Check and adjust web element contrast in real time.
EIII Checker Suite - The checker services can help you to locate and remove barriers on webpages or in PDF-documents.
Koa11y - Automatically detect accessibility (a11y) issues on webpages
Colordot for iOS - A color picker for humans.