"Icons do with color what Scripture does with words"; or, more accurately, "That which the narrative declares in writing is the same as that which the icon [(ἡ ἀναζωγράφησις)] does [in colours]."

"Modern viewers of art tend to see form in terms of line. . . . Gregory, however, expresses a late antique belief in the manifestation of form and reality through color[, a belief] that persisted throughout the Byzantine period."

     Liz James, "Color and meaning in Byzantium," Journal of early Christian studies 11, no. 2 (Summer 2003):  226 (223-233).  The lines immediately preceding, from pp. 225-226, are these (there is much more of great value):

     [Following classical philosophy,] The church fathers also perceived a significant role for color in making an image vital.  In his First Sermon on the Song of Songs, Gregory of Nyssa linked the creation of form to the use of colors[, speaking of] '. . . the form which the artist has created in colors.'  Colors direct the viewer to form:  they make it possible to apprehend form.  In case this should be seen as mere rhetorical flourishing and the display of cliché, John Chrysostom was even more explicit, implying that the image is not present until it is colored.  'As you see these things [the subject of the painting] being sketched, you do not know the whole, and yet you are not entirely ignorant of it, but you know faintly that a man and a horse are being drawn.  Who the emperor is, and who the enemy, you do not know exactly until the true colors have been applied, making the image clear and distinct.' . . . 'As long as somebody traces the outline as in a drawing, there remains a sort of shadow; but when he paints over it brilliant tints an lays on colors then an image emerges.'  On a spiritual level, this true likeness is Christ. . . . the sketch represents the shadow, that is, the Old Testament, and the true colors represent truth, that is the New Testament. . . .
. . . what Chrysostom says makes it clear that color was the more important element, without which an image was incomplete (and thus a false likeness) and unfinished.  This image of the underpainting preceding the colored picture that is the true image is one which recurs in the Fathers, from Cyril of Alexandria to Patriarch Germanos and John of Damascus, who described Melchisedek as the σκίασμα of Christ, the underpainting preceding the colored picture.
    This appears to express a widely-held and consistent belief that color gave an image form and reality.

Headline from the sixth session of the Second Council of Nicaea (i.e. Fr. Stephen Freeman and Daniel J. Sahas (Icon and logos:  sources in eighth-century iconoclasm:  an annotated translation of the sixth session of the seventh Ecumenical Council (Nicea, 787) (Toronto:  University of Toronto Press, 1986), 69) respectively).
     Thanks to Ben McFarland for putting me onto this emphasis on color specifically, via the Freeman version of those words.