For flowers, cut each marshmallow in half using clean kitchen scissors. Dip green marshmallow halves into green sanding sugar; dip yellow marshmallow halves into yellow sanding sugar. The sugar will coat cut edges of marshmallows. Place dime-size dot of frosting in center of each white square on cake. Arrange 5 marshmallow “petals” into flower shape, sugared-side-up, on top of each frosting dot; press to adhere. Press yellow sugar pearl into center of each flower. Store cake loosely covered.