... If you compare the first figure to the third figure, you can compare the Ektachrome with Kodachrome. You can immediately see that the curves of the 3 Kodachrome dyes are NOT matched, and that the Cyan is considerably higher than the other two. As a result, a visual neutral may look cyanish. To see why I say “may” look at the 4th figure which is a unit neutral of the Kodachrome dye set. You can immediately see that the cyan dye requires more density to give a visual neutral of 1.0 due to the fact that the cyan dye is very narrow in absorption. It is also low in unwanted densities and this introduces a big dip or gap in the neutral at about 600 nm. The lower unwanted absorption of the cyan in the green and blue region of the spectrum are responsible in part, for the improved overall color saturation. ... PE
There is one key difference between the two visual density diagrams: the Ektachrome dye absorption is adjusted for daylight (5000 K), while the Kodachrome is balanced for tungsten light (3200 K), so that excess cyan has to compensate the red bias in the warm light of a projector lamp. The human eye readily adapts to that difference in the color balance, especially at "ambient darkness" as required for a slide show.
On the viewing light table (or for reproduction by scanning and offset printing), the grey balance especially of Kodachrome 25 appears visually very neutral and accurate, with an excellent differentiation in brightness and hues. Kodachrome 64 might look slightly cooler, but it isn't bad either. ;-) The slight inconsistency of the different production batches of amateur Kodachrome as well as the shift towards magenta with age and storage conditions makes accurate comparisons somewhat problematic.
This was also the reasion for the introduction of professional Kodachrome, which hasn't been manufactured any more for years now - PKM 25 was discontinued in 1999. I have read memories from a German mountain photographer that the Kodak office at Stuttgart, Germany, had tested pro film batches to recommend matching emulsions for color consistency - in the 1980s.
I would judge color slides only by their impression on the standardized light table or from the spectral or at least colorimetric accuracy of a standardized color target.
I am still hoping for some nice sunny autumn days in the remaining two months, as I have still several rolls of 25 and 64 to feed into my manual Nikons. I now send envelopes with 19 films to the Stuttgart office and get back a parcel with the processed uncut rolls about two weeks later.