Contrast
A macOS app for quick access to WCAG color contrast ratios → https://itunes.apple.com/de/app/contrast-color-accessibility/id1254981365?l=en&mt=12
Pika
… an easy to use, open-source, native colour picker for macOS. Pika makes it simple to quickly find colours onscreen, in the format you need, so you can get on with being a speedy, successful designer.