If any way possible maybe employing a hydrometer to measure the specific gravity of both liquids and then searching avenues to help compare or match other specific gravities of various liquids from companies that sell all kinds of chemicals, many of these companies list the numerous details of the products they sell, from specific gravities to latent heat, atomic structure, weight,etc.etc. Some details of those lists include also solubility with other components, knowing specific gravities of different dye would also help. I guess what I'm trying to say is why not reverse engineer so to speak or use the tools we apply to come up with solutions for the same situation with our distraction ; Lava lamps, just a crazy thought. There's a link on this site to companies that do exactly what you're looking for chemicals and heaps of them, I'll check my favorites links to let you know, found it one.
http://www.engineeringtoolbox.com/liquids-densities-d_743.html. Hope this helps.