Combine vinegar and baking soda in a small bowl.
When the mixture stops fizzing, add corn starch and corn syrup. Blend together; the mixture will have a thick syrup-like consistency.
Divide the mixture among 3 small bowls.
For each colour, blend in a few drops food color. Mix with a paintbrush. Note: The more food colour you use, the more intense the colours will be.
Use the colours immediately, stirring frequently. Note: If paints dry up, simply swirl a paintbrush moistened with water and start painting. Finished painting should dry in 5 to 10 minutes.
TIP: For extra easy clean up, use a styrofoam egg container to mix the paints. Children will also enjoy experimenting with mixing food colours to create different colours.