In a large saucepan, melt unsalted butter (3 tablespoons) over low heat. Add marshmallows(4 cups) and stir until completely melted. Remove from heat.
Add Rice Krispies cereal (6 cups). Stir until well coated.
Press mixture into bottoms of snow cone cups. Shape top dome and press on top.
Melt white candy melts according to instructions on packaging, dye with food coloring, and spoon on top of snow cones. Immediately after coating, sprinkle on sanding sugar.