In the example I cited...
http://www.calliope.free-online.co.uk/abduct/pic20.htm
...the halftones on the neck are gray, turning into the black of the shadows -- an interesting effect, but not a realistic rendering of living flesh.
In fact, gray halftones have often been used in contrast with reddish to indicate dead bodies, typically that of Christ, as in this work by Rubens...
http://www.getty.edu/art/collections/objects/o1047.html
...note how the red blood of life has spilled from his wounds (and how the trauma is killing his mother, her face being drained of blood vis a vis her companions).
Art, of course, is always a matter of personal taste -- and I, too, also appreciate even grayish halftones when not taken to extremes -- but to my mind some of the most beautiful fleshtones were rendered by Boucher, as in his "Diana Leaving Her Bath" (unfortunately yellowed over time).
I have attached a detail scanned (in Fair Use, for comment and criticism) from a book -- the magnification is so great that you can begin to see the individual dots of (CMYK) ink (as I saw once at enormous magnification on a banner at the Los Angeles County Museum of Art): Boucher's hallmark "peaches and cream" complexions made use of almost the entire spectrum, with yellow predominating in the (sunny) highlights, red in the (rosy) halftones, and -- yes -- blue in the (relatively cool) shadows.
The primary colors again!
Although of course, still in mixtures -- even the warmest of brown shadows contain some blue, or else they'd be orange; and so forth.
And as you pointed out, Karin, by subsituting blacks for blues, the effects of colors are relative, so very dependent upon their surrounding colors.
But that's why I started this "primary colors" thread (now fairly "tattered"): I wanted to know if I was "off base" by staying with the old "red, blue, yellow" mindset -- if we don't know the elements, we can't compose good designs.