Color Science differences

Yes, but again that leads to a discussion that possibly most non-mathematicians would not follow.

Again, monochrome is spiky, it's not the only spiky.

Design is always a technological compromise. Clearly the design intent was a single spike in each channel. Frankly, knowing how this technology works, and how old the paper was, I'm very surprised that it's that good.
Anyhow, I'm getting the impression that you're seeing this more as a mutual urination contest between you and I than an attempt to clarify this whole matter for people who perhaps don't have the mathematical background that you do.

It isn't. Sorry if that disappoints you.

Thank @JACS and @bobn2 for explanations!

Actually I know, what is linear transformation, what means linearly independent and so on, I just get mental block everytime when I read about infinite dimensional spaces :) Or super unitary goups and similarly abstract algebraic concepts.

I'll attempt to explain in few words, what I gathered from this discussion (assuming linear model for all operations).

(1) image (incl. color information) is recorded by sensor in three channels, whose sensitivity is designed to [approximately] satisfy LI condition (linear combination of cone response); this process is subject to metamerism errors (or metamerism according JACS terminolgy)
(2) recorded data is converted into some RGB space, using linear transformations
(3) RBG data is used to produce output (screen or print), which (within device gamut) generates similar eye response as original scene

In non-linear case conversions (2) are a bit more difficult, but general idea is same.
'Color science differences' are mostly (a) different metamerism errors in different cameras/sensors in step 1 and (b) manufacturer preferred color tweaking models in step 2.
(I recall reading article from one Nokia designer, who told about tweaking Nokia's colors for months to get really pleasant image.)

PS. About Foveon - in first approximation image data is processed using linear transformations, it is seen in dcraw code for example. (I've coded Foveon software for older cameras after all :))

Interesting.

Nice summary for the TLDR folk.

Don't :) After few unsuccessful attempts I at last began to understand your 'infinite dimensional spectral densities' (as an infinite set of all possible spectral density functions over entire visible spectrum) - and now you turn my understanding upside down again :(
🙃