This would be fun, very easy, and general way to illustrate densities. Use water and food coloring showing how it mixes and the water turns colors then do this experiment showing how the oil does not mix by mixing the color in the oil first... fun fun fun
Take a salad spinner. Cut black paper to size. place inside & splat different coloured ready mix paint in side. Replace lid & spin! Instant picture (Guys Fawkes Night or Divali) and great for Physical development too!