3 Moreover, it seems that the Blessed Virgin Mary herself wished to confirm by some special sign the definition, which the Vicar of her Divine Son on earth had pronounced amidst the applause of the whole Church. For indeed four years had not yet elapsed when, in a French town at the foot of the Pyrenees, the Virgin Mother, youthful and benign in appearance, clothed in a shining white garment, covered with a white mantle and girded with a hanging blue cord, showed herself to a simple and innocent girl at the grotto of Massabielle. And to this same girl, earnestly inquiring the name of her with whose vision she was favored, with eyes raised to heaven and sweetly smiling, she replied: "I am the Immaculate Conception."
Source: Fulgens Corona (Vatican.va)