Imiscible fluids for demonstration
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...