Pour milk (full cream) into a dish.
Add a few drops of food-colour (red/yellow/blus) in separate areas of the bowl.
Squirt in some dish liquid.
Sit back & watch as the colours swirl & merge & mix.
Magic!
Hmmm, the milk we happened to use was low fat (it's the mix of the fat in the milk & the detergent that makes this magic happen) & the colours being watered down meant that it didn't really work this time but I was so impressed that Hug had remembered it!
Definitely worth a try if you happen to have spare colours after doing your eggs. I found this link to the same experiment if you want a bit more detail. I first discovered it for myself when I went to a Montessori 'Journey & Discovery' weekend. So much fun!