1.Grease a 20cm x 30cm rectangular pan; line base and long sides with baking paper, extending paper 5cm over sides.
2.Combine marshmallows and butter in medium saucepan. Stir over medium heat until smooth.
3.Place rice bubbles and half the rainbow chocolate chips in a large bowl. Add marshmallow mixture, mix well. Using wet hand, press mixture firmly into pan, then sprinkle with remaining rainbow chocolate chips. Refrigerate 2 hours or until firm before cutting.