Imiscible fluids for demonstration I have been considering building a fluid dynamics demonstration.  Basically, it would be a thin plexiglass box, with some turbulence inducing elements attached to the back face, and a pump to move the fluid around.

Can anybody recommend a pair of fluids that will:


not mix/dissolve permanently
can be dyed different colors, while respecting (1)
won't react with plexiglas (or, alternatively, polycarbonate)
isn't toxic or particularly flammable
can be pumped with a "very" low power pump at temperatures suitable for humans (say, 60-100F)


The point of the demonstration is to create a "sustainable" chaotic system.  I might even point an HD camera at it, and extract random numbers from the video stream (maybe).
Have a look at this paper

Summarizing: 


put food coloring to 35% isopropyl alcohol in water.
add ammonium sulfate


What happens ? Once ammonium sulfate added and the solution mixed, the ammonium sulfate dissolves, pushing the isopropyl alcohol out of the aqueous solution (and the food coloring as well).

A separate layer thus forms, that is clearly visible thanks to the food coloring.

The weak point of the whole story is that isopropyl alcohol is flammable...

PS: I would have preferred to reply to @Michiel's answer and @Nicolau Saker Neto's comment: but I do not have enough reputation to do that...