The mixture that is used is commonly used for paper-machie and consists of only flour and warm water.
1. Fill a container part of the way with warm water.
2. Slowly add flour to the water and stir.
3. Keep adding flour and mixing until you get a mixture much like paste.
That's all there is to the mixture.
To make different colored mixtures, just add a few drops of the food coloring in and mix.
Now that wasn't hard....
You can also use highlighter water to create a blacklight mixture: https://www.instructables.com/id/EU4KXH7QP3ES9J6OQQ/
(Last two pictures)...