Children press their fingers on inkpads or in paint then onto paper.
It gets absorbed by the towel, creating a sort of paint pad. Allow them to add water till the mixture becomes runny. They can then use brushes to paint with it or squeeze it from bottles or tubes onto dark paper. Add food coloring or colors of dry tempera if you wish. Spoon it into small bowls and allow the children to stir in their choice of liquid tempera paints, then fingerpaint with it.