Very cool that you did research on photoreceptors! I am not sure what you mean with "this space" which is supposed to be "closer to the truth". Can you elabor

Very cool that you did research on photoreceptors! I am not sure what you mean with "this space" which is supposed to be "closer to the truth". Can you elaborate? I am pretty sure I made no claims in that direction[1]. What I am saying is that modeling human color perception as a three-dimensional space is sensible, given the fact that we tend to have three color receptors with different spectral sensitivity. Similar physiological reasons apply for the CIE Lab space. Yes, it is a mathematical construct, but it is a reasonable mathematical construct. My color theory has been a while, but my understanding is that there is some pre-processing of the raw photoreceptor inputs that means the signals arriving in the brain are differential signals like the red-green difference (a) and the yellow-blue difference (b) of CIE Lab. And of course we get the luminance from the non-color receptors separately, though of course the signals are correlated. So how we interpret a specific (a) signal depends on what L is. So there are good pragmatic and scientific reasons for most of the proposed color spaces, but they are all compromises and driven by different pragmatic needs. They tend to be based on CIE XYZ, which defines a "standard observer". Is your objection this definition of a "standard observer"? To me, the very fact that such a "standard observer" is defined and called that makes it pretty clear that this "standard observer" is not the "universally true observer", but rather a useful fiction. And again, not an arbitrary fiction, there are reasons for choosing that particular one, but I don't see any claim to universal truth. I am still somewhat puzzled by your mention of metamerism as only applying to the color yellow. [1] I did single out CIE Lab, but clearly marked that as a purely personal preference.