I wanted to paint some of my mirkwood rangers with dark angels green, but it had dried out. So, I went to my nearby Warhammer store and bought a pot of the contrast dark angels green (not a real color match BTW) and tested it on one of the rangers. I was pleasantly surprised at the effects. At one point I needed a break from working on 60 mirkwood miniatures. So, I, as others, thought about a way to make a contrast paint out of any regular paint since I liked the effect but already have 50+ bottles of paint. I searched around the interwebs and tried some various diluents with some success. Though none really had the viscosity of the contrast paints. I had some extra matte gel from another project so I used some of that in a new diluent. I used roughly 20% of the matte gel and then added water with a couple of drops of liquitex flow aid. This is essentially what I dilute my paint with, except I use golden airbrush medium about 1:3 with water. I do primer my minis dark gray with a zenithal white highlight normally but these are just white. The results are below, 1:5 vallejo purple paint to either the water (left) or the new diluent (right).
Not really going to comment on it other than it seems to work differently between the ink and the paint.