Trying to identify the ink binder...

[Jorge_Stolfi]

If we assume the VM came from an amateurish and not exactly wealthy background, it's not far fetched that the creator(s) chose DIY approaches over commercial ingredients like Gum Arabic. Cherry or plum gum would fit into this picture, as well as the overall unusual ink composition.

But don't forget that there is no good evidence that the colorpaint are contemporaneous with the text, while there is some evidence (the page number covered by green paint) that the color paints are quite a bit later. 

Still, I share the feeling that the Painter too was a (rather sloppy) amateur who improvised his paints.  The McCrone report apparently says so for the green paint.  His blue paint uses azurite, a standard blue mineral; but it does not seem to be finely ground (as a paint pigment should be), and it seems that he mixed it with some dark substance that failed to dry out, collected along the edges of the painted area, and then left dark stains ("offsets") on the facing pages.   

All the best, --stolfi