Palette for Mac is described as '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)' and is an app in the Photos & Graphics category. There are four alternatives to Palette for Mac for a variety of platforms, including Online / Web-based, PortableApps.com, Self-Hosted solutions, Windows and Firefox. The best alternative is Who Can Use, which is both free and Open Source. Other great apps like Palette for Mac are Colour Contrast Analyser (Free), Wave (accessibility tool) (Free) and Cron Color (Free).
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.