[piannucci]

I love the drama of how the abstract is written, but TBH I don't think this is a surprise. I believe it's well-known among color theorists that large perceptual distances are inconsistent with sums of small differences. So maybe the most generous thing to say here is, good on them for bringing awareness of this subtlety to a broader audience.

[mpweiher]

Not only that, it is also well known that the smallest perceptible color difference (ΔE=1) is not actually consistent, even in the "perceptually uniform" color spaces.

So ΔE is actually 1 in some parts of the space, but up to 4 in others. However, that is "good enough" for the purpose for which these color spaces were created: quality standards for color ("can I buy more of the same color and it will look the same?"). If your measured and computed ΔE is below one, the difference will not be perceptible by most humans regardless.

And last I checked, new and improved "perceptually uniform" color spaces are proposed every couple of years.

[robwwilliams]

Yep: color space is a pragmatic kludge not a “real thing” divorced from the human neural network that is its fundamental basis.