He has undoubtedly done in his hues what he has done in the arrangement of the work.

His picture is a hymn to Chastity, and round the central group of Christ and His Mother he has placed in ranks the Saints who best concentrated this virtue on earth.

St.John the Baptist, beheaded for the bounding impurity of an Herodias; St.George, who saved a virgin from the emblematic Dragon; such saints as St.Agnes, St.Clara, and St.Ursula; the heads of the Orders--St.Benedict and St.Francis; a king like St.Louis, and a bishop like St.Nicholas of Myra, who hindered the prostitution of three young girls whom a starving father was fain to sell.

Everything, down to the smallest details, from the attributes of the persons represented to the steps of the throne, of which the number is nine--that of the choirs of angels--everything in this picture is symbolical.
It is permissible therefore to assume that he selected his colours for their allegorical signification.
White: the symbol of the Supreme Being, and of absolute Truth, and employed by the Church in its adornments for the festival of our Lord and the Virgin because it signifies Goodness, Virginity, Charity, and is the splendour, the emblem of Divine Wisdom when it is enhanced to the pure radiance of silver.
Blue: because it symbolizes Chastity, Innocence, and Guilelessness.
Red: which is the colour adopted for the offices of the Holy Ghost and of the Passion; the garb of Charity, Suffering and Love.
Rose-pink; the Love of Eternal Wisdom, and, as Saint Mechtildis teaches, the anguish and torments of Christ.
Green: used liturgically at Seasons of Pilgrimage, and which seems to be the colour preferred by the Benedictine Sisterhood, interpreting it as meaning freshness of soul and perennial sap; the green which, in the hermeneutics of colour, expresses the hopes of the regenerated creature, the yearning for final repose, and which is likewise the mark of humility, according to the Anonymous English writer of the thirteenth century, and of contemplation, according to Durand of Mende.
On the other hand, Angelico has intentionally refrained from introducing the hues which are emblematic of vices, excepting of course those adopted for the garb of the Monastic Orders, which altogether changes their meaning.
Black: the colour of error and the void, the seal of death, and, according to Sister Emmerich, the image of profaned and wasted gifts.
Brown: which, as the same Sister tells us, is synonymous with agitation, barrenness and dryness of the spirit, and neglect of duty; brown; which being composed of black and red--smoke darkening the sacred fire--is Satanic.
Grey: the ashes of penance, the symbol of tribulation, according to the Bishop of Mende, the sign of half-mourning formerly used in the Paris ritual instead of violet in Lent.

The mingling of white and black, of virtue and vice, of joy and grief, the mirror of the soul that is neither good nor evil, the medium being, the lukewarm creature that God spueth out, grey can only rise by the infusion of a little purity, a little blue; but can, when thus converted to pearl grey, become a pious hue, and attempt a step towards Heaven, an advance in the lower paths of Mysticism.
Yellow: considered by Sister Emmerich as the colour of idleness, of a horror of suffering, and often given to Judas in mediaeval times, is significant of treason and envy.