I'm a little surprised that colorchord didn't get a mention, since several folks use it for chromatic sound analysis to color conversion. ColorChord .NET (the desktop music visualizer) as well as AudioLink in VRChat both use the ColorChord core for the chromatic mapping. There was a really good interview with Macyler from CC.net on youtube a few years back.

There's so many massively better solutions than FFTs when it comes to the way people perceive sound.