poster paint 
noun [mass noun]
An opaque paint with a water-soluble binder, used for posters and children’s paintings: it was done using poster paints and gouache [mass noun]: that powdery poster paint kids use...
- Crayon, oil, colored pencil, and poster paint lend the work a saturated, hyperbolic sensibility.
- Mix up pots of poster paint, and give your children a pot of paint in each colour, a couple of brushes and a glass of water.
- The vandals had covered the floors in powder paint and sprayed walls with poster paint.