Kontrast is a color contrast checker that tells you if your color combinations are distinct enough to be readable and accessible. It is part of the Plasma Mobile app collection.
Colour Contrast Analyser allows you to evaluate the color visibility and contrast of foreground/background color combinations. It provides an initial pass/fail assessment against WCAG 2.0 color contrast success criteria.
Palette provides a super simple way to analyze colors across RGB, #HEX and CSS formats. Try it online for free or download it for macOS with a donation-based download where you pay what you want (even $0 to try it).