The landing page doesn't seem very exciting (on mobile at least) but the "practice" area of the site contains quite a few web apps to demonstrate the concepts. I think the basic idea is that western music uses 12 tones, and chromatone gives each of those tones a color, and uses those 12 color/tone pairs as a basis for teaching music theory in a visual way.
And also here's where I found a lot of additional web apps. I'll look through them more when I'm at my PC. But just thought I'd post these here for anyone who clicked on the hn link but was underwhelmed or confused by the landing page:
https://chromatone.center/practice/
Here's a simple app that works on mobile (android/chrome anyway): https://see.chromatone.center/
And also here's where I found a lot of additional web apps. I'll look through them more when I'm at my PC. But just thought I'd post these here for anyone who clicked on the hn link but was underwhelmed or confused by the landing page: https://chromatone.center/practice/
https://chromatone.center/practice/experiments/
https://chromatone.center/practice/sound/