'Red' in the Bible

when we invade the land, if you don't tie this rope made with red cords in the window through which you let us down, and if you don't gather your father, your mother, your brothers, and all of the rest of your father's household into your house.

"Since you put it that way," she replied, "I agree." After she sent them on their way and they had left, she tied the red cord in the window.