There seems to be some confusion in earlier posts in this thread on color accuracy of slides vs. color negatives and the function of the mask in color negatives.
The dyes used in both slides and color negatives have impurities which degrade colors. These impurities are not that noticable if the dyes are used once, in other words viewed directly.
But if an optical print is made from either, then the dyes are used twice (since the print material has dyes with impurities as well) and the problem compounds. Now the impurities are very noticable unless they are somehow corrected.
If we can remove the impurities from either stage, then reasonably good color results in the print. In a negative, we mask the impurities (which are collectively orange in color) with a positive mask (also orange in color), effectively canceling the impurities and a good print results after the orange is filtered out.
With a slide, we can't do this and thus a print from a slide that is not masked in any way will have degraded colors compared to a print from a masked negative, as well as having high contrast.
In publications, when slides are used, masks can be, and usually are made to correct impurities and lower contrast, and used at the printing stage which is why good color can result. This could also be done when optically printing slides.
In scanners, any color errors in the scanning system (comparable to the dye impurities in print material) is likely taken care of in the software which is why slides can be reproduced faithfully. If one has a problem scanning color negatives, then the problem is in the scanning system or its setup, not with the negative, assuming it was exposed and processed correctly.
At the lab I work at, we used to scan negative film before we went all digital and the scanners, which were Kodak scanners and setup by Kodak, could give beautiful results. But different films, having different dyes and masks, required different setups or channels for each, to give the most accurate results.
