Digital BW, The Print

>... the fact that different coatings create different hues with mono ink should be a major clue that something delicate, and potentially problematic, is happening chemically at that bond. ...

I'm not sure whether there is a chemical bond involved.  

Another hypothesis is that the way in which pigments are absorbed or spread could affect the hues we see.  For example, with respect to the blended carbon + color inks, which include the Piezo inks (aside from the carbon sepia), the different pigment types could be absorbed differently on the coating.  Early on the way we could tell that an ink was not 100% carbon was to put a drop onto a piece of paper and the colors would spread and show -- a form of "paper chromatography."  With the 100% carbon pigments the warmth seems to be an edge affect mostly.  Where a paper spreads the ink more, causing more of the edge to be semi-transparent, there might be more warmth.  Where the droplet is tightly held and does not spread or bleed, there might be less warmth.  This might affect the mostly carbon blended Piezo inks as well.

Paul
www.PaulRoark.com