Wandering about the Midwest, often come upon a church with a very Red Door.
Must be a reason for this. This Red Door effect is not limited to a single denomination as it can be found on churches supporting a variety of beliefs.
A rather brief search offers many reasons. Of the several answers, found
"The red door tradition goes back to the beginnings of cathedral architecture in the Middle Ages. The color red, signifying the Blood of Christ, was painted on the north, south and east doors of a church. Such symbolism represented making the sign of the cross -- Father, Son and Holy Ghost. Thus the edifice was marked as a sanctuary, identified as a refuge and safety zone from physical or spiritual dangers. The red doors shut out evil. Supposedly an enemy could not pursue his victim across the sacred threshold."
Mary S. Holley
to be my favorite. Sounds simple, direct and reasonable.
Works for me.