So much about the color of Mars is both subjective and a matter of definition. On the subject of the sky color, Dr. Maki observed in his paper:

The light to moderate yellowish brown color ... of the noontime sky near the horizon is consistent with the sky color seen at the Viking sites [Huck et al., 1977]. The sky color varies as a function of time of day and azimuthal look angle (Figure 5). Figure 5 also shows that the sky is slightly redder in the anti-Sun direction and bluer in the direction of the Sun. This relative change in color is at the limit of perceptibility and would probably be difficult to notice with the naked eye while standing on the Martian surface.

...

The color of the sky at sunrise and sunset is considerably different from the color of the noontime sky near the horizon. The sunrise/sunset sky has average chromaticity values ... which correspond to a grayish olive color ... or a brownish gray color... This sky color becomes bluer toward the Sun, transitioning gradually from brownish gray at 15° to a bluish white color ... 5deg; from the Sun. At 2deg; from the Sun the ... chromaticities ... correspond to a very pale blue color ... or a very light blue ....

(Emphasis added; ellipses are technical data removed for clarity)

I don't think Maki and NASA completely deny that the sky is blue; rather, they're saying that there's some blue in it but you wouldn't be able to easily distinguish it from the dominant brownish using the naked eye. How much blue depends on where you look, and of course on dust in the atmosphere.

Here's one of the sky images from Maki's paper; this is his "TrueColor(natural)"

If you greatly exaggerate the saturation ("color contrast"), you can see the blue:

the reason why NASA never did much work on color correction is that they did not mind giving Mars a clear blue sky in their press releases - after all, NASA needed to foster the illusion of an Earth-like Mars to justify their institutional existence.

I'm not so sure about that. I can't recall an official release with a blue sky, and in fact their "failure" to come through with the blue has gotten a lot of people made at NASA over the years. OTOH, I've noticed you're pretty down on a habitable Mars--might you be just a tad bit prejudiced, Ed? Hmmm?

Overall these latest images are well-calibrated, and it looks like they're giving a lot of attention to monitoring the sky color, presumably for the purpose of accomplishing exactly what you describe: Calibrating the spectra from the images to get accurate geologic data. Seems like half the images are calibration of some kind, sundial or Sun or atmospheric studies.

Well, I've been rambling a lot, so I'd better wrap it up. Glad you're enjoying these images, I know I sure am.