Occurrences in the Bible
The English word "scarlet" is recorded 52 times in 52 King James translation verses. It is found 46 times in 46 Old Testament verses and 6 times in 6 New Testament verses. It appears the most in Exodus (26 times) followed by Leviticus (5) and then Revelation (4).
The Hebrew words tola (Strong's Concordance #H8438) followed by shaniy (#H8144) are translated as "scarlet" 27 times in 27 verses. When these two words are swapped (shaniy tola) they are translated as this color another six times in six verses.
Both Shaniy and Tola can refer either to scarlet directly or to the dried body of the female maggot (worm) from which the dye was extracted. Shaniy by itself is translated as "scarlet" six times in six verses. It is also, by itself, rendered as "scarlet thread" in Genesis 38 verses 28 and 30. Tola by itself is written as this color only once.
They that did feed delicately are desolate in the streets: they that were brought up in scarlet (tola) embrace dunghills. (Lamentations 4:5, KJV).
In the book of Daniel, the Chaldee word argvan (Strong's #H711) is translated as "scarlet" in Daniel 5:7, 16 and 29. Lastly, the Hebrew tala (#H8529) is translated as "scarlet" only in the writing of the minor prophet Nahum. The word means to wear clothing with this color.
The shield of his mighty men is made red, the valiant men are in scarlet (tala): the chariots shall be with flaming torches in the day of his preparation, and the fir trees shall be terribly shaken. (Nahum 2:3, KJV).
The Greek word from which "scarlet" is derived in the New Testament is kokkinos (#G2847). It refers to the kernel shape of the insect from which the pigment is extracted.
Background
Scarlet has an HTML hex code of #FF2400. It is a color with an approximate wavelength of 608 nanometers.
Egyptians obtained this pigment for dyeing from a shellfish while the Hebrews extracted it from an insect (the kermes) that infests oak trees. The color is so steadfast that it was one of the most difficult dyes to remove from clothing.
Scarlet has conveyed the meaning wealth and power, both politically and religiously, since ancient times. Second only to purple, it was a status symbol in the mighty Roman Empire. Officers in Rome's army wore cloaks dyed in it as well as high-ranking non-military people. The flag carried by the Crusaders during the Middle Ages displayed a cross in scarlet.
Since the late 13th century Roman Cardinals, who are high-level religious leaders in the Catholic Church, use scarlet for their ecclesiastical clothing.
Biblical Symbolism
This color can symbolize high quality. One of the things God commanded the ancient Israelites to donate for the tabernacle in the wilderness is scarlet.
Speak unto the children of Israel, that they bring me an offering: of every man that giveth it willingly with his heart ye shall take my offering. And this is the offering which ye shall take of them; gold, and silver, and brass,
And blue, and purple, and scarlet (tola shaniy), and fine linen, and goats' hair . . . (Exodus 25:2 - 4, KJV).
This color found its way into the tabernacle's curtains, vail, the hanging used for the tent's door, the court gate and so on (Exodus 26:1, 31, 36, 27:16). The holy garments worn by Aaron the High Priest also had scarlet (Exodus 28:5), including the ephod, the ephod's girdle and breastplate he would wear (Exodus 28:6, 8, 15, etc.).
Scarlet can additionally symbolize wealth, power, prosperity or prestige. Daniel was clothed in garments of this color by the Neo-Babylonian Empire's last ruler after he interpreted the "handwriting on the wall" (see Daniel 5:25 - 28).
Then commanded Belshazzar, and they clothed Daniel with scarlet (argvan), and put a chain of gold about his neck, and made a proclamation concerning him, that he should be the third ruler in the kingdom (Daniel 5:29, KJV).
The virtuous woman of Proverbs 31 is diligent and prosperous enough to insure her family is clothed with the best.
She is not afraid of the snow for her household: for all her household are clothed with scarlet (shaniy). (Proverbs 31:21, KJV).
Scarlet can also symbolize sin. In Isaiah 1:18 the word shaniy is rendered as "scarlet" but tola by itself is translated as the color crimson.
Come now, and let us reason together, saith the Lord: though your sins be as scarlet (shaniy), they shall be as white as snow; though they be red like crimson (tola), they shall be as wool. (Isaiah 1:18, KJV).
Scarlet is lastly the symbol of royalty. Pilate, unable to set Jesus free due to the crowds, condemns him to death on the cross. He sends him to his Roman soldiers who scourge him and then dress him with a scarlet robe. This is done to mock the claim that Christ was the King of the Jews.
And they stripped him, and put on him a scarlet (kokkinos) robe.
And when they had platted a crown of thorns, they put it upon his head, and a reed in his right hand: and they bowed the knee before him, and mocked him, saying, Hail, King of the Jews! (Matthew 27:28 - 29, KJV).
The Prophetic Harlot in Scarlet
The great harlot of Revelation is said to not only be riding a beast that is the color scarlet but also dressed in it! She represents the world's false religious systems who, instead of promoting the truth, teach deception and disobediance to God.
Then he carried me away in the spirit to a wilderness; and I saw a woman sitting upon a scarlet beast that had seven heads and ten horns, full of names of blasphemy.
And the woman was clothed in purple and scarlet, and was adorned with gold and pearls and precious stones; and she had a golden cup in her hand, filled with abominations and the filthiness of her fornication;
And across her forehead a name was written: MYSTERY, BABYLON THE GREAT, THE MOTHER OF THE HARLOTS AND OF THE ABOMINATIONS OF THE EARTH. (Revelation 17:3 - 5).
Why a Scarlet Thread?
In Genesis 38 we find a curious event involving a scarlet thread.
Briefly, a woman named Tamar, who was the daughter-in-law of Judah (one of the sons of Jacob), got pregnant through Judah by pretending to be a harlot. When it came time to give birth, Tamar's midwife discovered that twins would be born. When one of the babies stuck his hand out of the womb, and looked like he would be the firstborn, the midwife tied a scarlet thread around his hand.
Anciently, a scarlet thread was commonly used to designate who was the firstborn. After receiving the thread, the baby quickly pulled his arm back in the womb! The other child to be born, also a boy, then came out of the womb completely!
The child who had the thread around his hand received the name Zarah and his twin brother received the name Pharez.
. . . when she (Tamar) travailed, that the one (baby) put out his hand: and the midwife took and bound upon his hand a scarlet thread, saying, This came out first. And it came to pass, as he drew back his hand, that, behold, his brother came out: and she said, How hast thou broken forth? this breach be upon thee . . . (Genesis 38:28 - 29, KJV).
What is the meaning of all this in relation to prophecy? Judah was destined, according to the Bible, to be the royal tribe of Israel from which rulers would arise (Genesis 49:8 - 10). It is through Pharez's descendants (the child literally born first) that not only King David is born but also Jesus Christ as well!