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