The most pure Virgin, dressed in white with a BLUE SASH, deigned to appear eighteen times resplendent with LIGHT, sweetness and beauty in the Grotto of Lourdes and to say to the humble child who contemplated HER in her ecstasy: “I am the Immaculate Conception.”

"O how hast Thou multiplied Thy mercy, O God! But the children of men shall put their trust under the covert of Thy wings. They shall be inebriated with the plenty of Thy house; and Thou shalt make them drink of the torrent of Thy pleasure. For with Thee is the fountain of life; and in Thy light we shall see light" -- Psalm 35:8-10.

"the water that I will give him, shall become in him a fountain of water, springing up into life everlasting" -- John 4:14.

"He that believeth in Me, as the Scripture saith, Out of his belly shall flow rivers of living water" -- John 7:38.

In looking at the Lady in the Niche, we see the "living water" flowing as "a fountain" from her virginal womb symbolized by the blue sash and the torrent of water that now flows abundantly from the Grotto. In consecrating ourselves to this Living Ark of the New Covenant, we can drink freely of this living water come under the cover of His Wings to see His Light, the Light of light, the very source of light, in her light.

"The earth is the Lord's and the fulness thereof: the world, and all they that dwell therein. For he hath founded it upon the seas (maria); and hath prepared it upon the rivers" -- Psalm 23:1-2.

"God the Father gathered all the waters together and called them the seas (maria). He gathered all His graces together and called them Mary (Maria)"—St. Louis de Montfort, True Devotion to the Blessed Virgin Mary, no. 23.

Surely these give us some reasons why BLUE is the color of Our Lady.

“Like our Predecessor, we ardently desire that Christendom be renewed in a unanimous élan of Marian piety, for, when it is understood according to the Church’s doctrine, it cannot but lead souls more surely and more quickly to Jesus Christ, our one and divine Savior. Following those Pontiffs who for a century recommended that Catholics pay attention to the message of Lourdes, we urge you to listen, with simplicity of heart and an upright mind, to hear the salutary warnings of the Mother of God – warnings still relevant today. […] Moreover, let nobody be surprised to hear the Roman Pontiffs insist on this great spiritual lesson passed on by the child of Massabielle. If they have been constituted guardians and interpreters of Divine Revelation, contained in Sacred Scripture and Tradition, they also have a duty to recommend to the attention of the faithful – when after mature examination they judge it opportune for the general good – the supernatural lights which it pleases God to freely dispense to certain privileged souls, not to propose new doctrines but to guide our conduct (cf. Saint Thomas, IIa-IIae, q. CLXXIV, a. 6, ad tertium.) Such is indeed the case with the apparitions of Lourdes…” (Pope John XXIII radio address, Feb 18, 1959, at the closing of the Centennial of Lourdes).

“Penance! Penance! Penance! Pray to God for sinners! Kiss the ground as an act of penance for sinners”—Our Lady of Lourdes.

“In our time,—as Christians have often had, and still have the opportunity to experience,—the august Mother of God makes Her presence felt in human events in a special way [e.g., apparitions like Our Lady of the Snows, Lourdes and Fatima]. The more charity grows colder, the more urgently this Mother exhorts Her children to piety, to virtue, to penance for sin; and when from every side the menace of fearsome scourges increases, we feel that in Her clemency She intercedes for us, that She implores for us mercy, warding off the chastisements merited by our faults. Thus we have a powerful patroness with the Divine Majesty, we have a Mother who with a heart full of pity has compassion on Her children’s sufferings. Hence, one would be placing his own salvation in jeopardy if, when he is assailed by the tempests of our world, he refused to accept Her helping hand.” (Pope John XXIII radio address, April 1959, a few months prior to his opening the 3rd Secret of Fatima).