Spread out a few sheets of wax paper.
In a large saucepan, melt butter or margarine over medium heat. Add marshmallows and stir until completely melted; remove from heat. Stir in rice cereal.
Lightly oil hands and any utensils (such s a spatula).
Scoop out about 1 cup of cereal/marshmallow mixture onto wax paper. Shape mixture into a triangle. Repeat until all mixture is finished.
In a microwave-safe bowl or cub, melt the yellow frosting for 20 seconds at 50% power; stir, and pour the yellow “stripe” onto each of the triangles. Repeat process with the remaining 2 colors. Refrigerate until set.