Interesting Mark. Skins and seeds are important in the flavor development in reds. And obviously, there are differences in the juice as well, as the white varietals are all different, but have no skin contact. As a matter of speculation, I wonder what would a wine taste like if it was, say Pinot Noir juice, fermented with, say Zin skins and vice versa?
Now for a digression. I made an interesting observation several years ago. I was making some Foch, an early ripening, deeply colored hybrid that were very ripe (25.5 brix). A few weeks later, I gently pressed out Vidal, a white hybrid at normal ripening of about 21 Brix. I added the hard pressed Vidal juice, pulp and skins to about half of the Foch - the other half I kept as a complete 100% varietal. After the wines completed fermentation, I was surprised to find that the one that had the Vidal pressings added actually had a deeper, more purple color. In addition, the 100% varietal actually declined quite quickly, whereas the blend kept for a longer time. I posed this dilemma to forumites here (the old WLDG - they provided links to studies) and learned that the pH has an effect on the color and hue of a wine and its stability. By adding the higher acid Vidal, I lowered the pH, which affected the overall quality of the wine.