From the abstract:
The scientific community generally agrees on the theory, introduced by Riemann and furthered by Helmholtz and Schrödinger, that perceived color space is not Euclidean but rather, a three-dimensional Riemannian space. We show that the principle of diminishing returns applies to human color perception. This means that large color differences cannot be derived by adding a series of small steps, and therefore, perceptual color space cannot be described by a Riemannian geometry.
I know from personal experience of being fooled on hundreds occasions when trying to judge colors, color temperature, etc. despite my experience and the fact that my color vision is normal (I've never failed any Ishihara or related tests).
The law of diminishing returns is essentially what I experience as an observer, the more I grind my observation fine the more fooled and less objective I become. I now only believe my instruments.
Thus it makes sense that large color differences cannot be derived by adding a series of small steps simply for the reason they are in effect a form of noise in relation to large steps.
"therefore, perceptual color space cannot be described by a Riemannian geometry."
Perhaps Riemannian geometry should become just a starting point if for no other reason than it serves to illustrate the complexity of human color perception and the difficulty it poses in trying to analyze it.
That may well be, but the title doesn't point to the overturning of some infantile color theory people believed 100 years ago.
It points to the overturning of a still dominant theory, that was first developed 100 years ago, but continues to be considered as the standard.
The article might be wrong in that that's the case, but that's how the title reads.
{*} This is not limited to perception. Attempts to described even small parts of reasoning, language and memory with simple models failed too, but that seems less surprising, since perception is closer to the physical reality.