This step is only necessary if your paper cup has prints on it or if it has a glossy surface. Priming the surface with white acrylic paint will hide the prints on the paper cup and allow the tempera or poster paint to adhere better to the surface of the cup.
To prime your paper cup, simply paint the outside of your cup with undiluted white acrylic paint.
Paint the paper cup with pastel shades of tempera or poster paint such as light blue, pink, or yellow. Leave the angel's hands unpainted.
You can mix your own pastel shade of paint by adding a bit of colored paint to white paint. For instance, you can come up with light pink by adding a tiny bit of red to white paint. To make light blue, add a dab of blue to white paint.