What you need:

- Plate with a wide rim
- Milk (about 1/2 Cup)
- Food colouring of different colours
- Washing up detergent

What to do:

1. Pour milk onto the plate (make sure it covers the whole surface of the plate)
2. Put a few drops of food colouring on the milk at different points
3. Put a drop of detergent on the rim so that it runs into the food colouring
4. Watch what happens and be amazed by the colours!

Why does it happen?

Surface tension normally holds things in place - for example the colour didn't mix in with the milk. It stayed put. But the washing detergent broke the surface tension and allowed the milk to move around. The colour simply displays how the milk moved.