I agree, but I'm surprised there was no mention of contrast or proposal to restrict colors.

Their first good example bumped up the color contrast. The orange examples in their set of "gorgeous app icons" are just as bad as the slack vs photos example.

I would love if the OS had an option to automatically convert every app icon to greyscale and required a minimum color contrast ratio for the original. Then, the user can pick their own overlay colors (similar to the color tags in finder).