The app’s download page on flathub claims it’s what Gotham needs right now. Maybe the developer is referring to Harvey from The Dark Knight.Harvey is a color checker tool for testing if the color of your foreground text against your background color content complies with WCAG A, AA, and AAA levels.
WCAG stands for Web Content Accessibility Guidelines. Its role is to keep the website accessible to everyone. There are three levels; namely A, AA, and AAA.The further the level, the harder it becomes to design your website ie., A guideline is much easier than AA and AAA, again AA is easier than AAA but more difficulty in implementation compared to A. But that doesn’t mean it’s compulsory for your website to be WCAG compliant.
Otherwise, for a terminal savvy person, you can use the below command to install the same on your computer: