This is a great alternative to using 'real' paint which can leave stains!
All you need is:
Plastic or old cups or glasses
1/3 cup of water (per colour you decide to make)
1 tablespoon of cornflour (per colour you decide to make)
Pour 1/3 cup of water into a plastic cup or glass. Then add 1 tablespoon of cornflour and 6 drops of your preferred food colouring. We made four colours Red, Green, Yellow and Blue, which the girls then mixed to make other colours (ie. purple, orange and dark blue).
This recipe makes a watery type consistency, which "runs" all over the place so you only need a very little amount (I'd tried telling my girls that!) at a time.