At the
Battle of Lepanto (1571), the navies of the Holy League (consisting of the Papal States, the Habsburg possessions of Spain, Naples and Sicily, the Republics of Venice and Genoa, the Grand Duchy of Tuscany, the Duchies of Savoy, Parma and Urbino and the Knights of Malta) faced off against the fleet of the Ottoman Turk. Both sides were backed by their religious leaders, Pope St. Pius V being the sponsor of the Holy League, and both the religious and political authority of the Ottoman Empire resting in the hands of Selim who was both Caliph and Sultan. And so the flag-ships of both armadas flew religious banners, both of which were understood to be the "color of Heaven."
The banner supplied by the Pope consisted of a golden crucifix upon a field of blue, and that makes sense because to a European, the clear blue of the sky would be the "color of Heaven."
The banner supplied by the Caliph consisted of the names of God stitched in golden embroidery upon a field of green, and that too makes sense because to Muhammad, a son of the desert, the verdant green of vegetation would be the "color of Heaven."
This is an important and telling cultural difference. We might further extrapolate that the "cultural characters" of Europe and the Muslim world now reflect these colors, the affluent West being blue with melancholy (or perhaps more accurately "acedia") while the stagnant East is green with envy and resentment.
Of course, these are generalizations, for every person has their own "color of Heaven." My Heaven is gray: the color of Chicago skies, the color of practicality, the color of contentment.