“Two-Worlds in Old Russian Icon Painting” from Icons: Theology in Color by Eugene Trubetskoi.
In other icons of the Dormition, other colors of the celestial range are used to achieve the effect of separation of the two planes. Christ standing behind the deathbed is separated from the Virgin not only by assist but also by a special coloration of the celestial sphere surrounding him. Sometimes a single sphere forms around him a dark blue oval in which cherubim are seen. All these cherubim seem too drown in the blueness—except one, flaming red at the apex of the oval above the Saviour’s head. Sometimes…the oval contains many celestial spheres, one above the other, distinguished from one another by a multitude of shadings of light blue, including some incredible greenish-turquoise tints. The impression of something literally “out of this world” is overwhelming. For a long time I worried over the question of where the artist could have observed such colors in nature—until I saw them myself, after sundown, in the northern Petrograd sky.
Part 4: Red