You will need: some skittles/smarties/m&ms. Coffee filter paper cut into strips or kitchen towel cut into strips, a small plate with a rim (you're going to put water in it).
Put hold a sweet into a tiny bit of water. Count to 20. Then place the sweet onto the bottom (about 1 cm from the end) and leave it to dry. Repeat 3 more times with different coloured sweets (we recommend 1 primary colour - red or yellow, then other colours - purple and green work well). You should have a small coloured circle where each of the sweets have been.
Have a chat with your children. Do they remember the colour mixing from earlier in the week? How do you make green/purple etc.
Now clean the water and hold the strip of paper just under the occurred circle in the water. Count to 60 - you should see the water absorbing up the paper. Now leave the paper to dry (and some sneaky sweet eating!)
Come back to the paper. Can you see how the colours have separated? You should see really clearly how the colours have been mixed.