Behold, when we come into the land, thou shalt bind this line of scarlet thread in the window which thou didst let us down by.... And she sent them away, and they departed: and she bound the scarlet line in the window (Joshua 2:18a & 21b).
Come now, and let us reason together, saith the Lord: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool (Isaiah 1:18).
Other Old Testament books that talk about the color or of the sea which is that color, are Leviticus, Numbers, Deuteronomy, Judges, 1Kings, 2 Kings, Nehemiah, Esther, Psalm, Isaiah, Jeremiah, Nahum, and Zechariah. However, Matthew, Acts, and Revelation also mention it in the New Testament. Red came to represent a blood sacrifice.
For this is my blood of the new testament, which is shed for many for the remission of sins (Matthew 26:28).