MELT butter in large saucepan on low heat. Add marshmallows; cook until marshmallows are completely melted and mixture is well blended, stirring constantly. Remove from heat. Add food coloring; mix well.
STIR in cereal. Press firmly into greased 15x10x1-inch pan. Cool completely.
CUT into heart shapes with greased 4-inch cookie cutters. Decorate with icings as desired.