'Scarlet,' as in Genesis 38:28, signifies spiritual good.

In Isaiah 1:18, this signifies truth derived from good, or truth from a celestial origin, such as is the truth of the Word in its literal and natural sense

'Scarlet,' in Revelation 17:3, signifies truth from a heavenly origin, such as is the truth of the Word in the sense of the letter or natural sense, which is meant by what is holy in it. 

(Referencat: Apocalypse Explained 67)

3636. It is an entirely general and all-embracing law that the Lord is the Sun of heaven and that this is the source of all the light in the next life; that nothing at all from the light of the world is visible to angels and spirits, that is, to beings in the next life; and also that the light of the world which comes from the sun is to angels nothing else than thick darkness. From the Sun of heaven, or the Lord, comes not only light but also warmth; but these are spiritual light and spiritual warmth. The light that strikes their eyes is seen as light but it holds intelligence and wisdom within it since it is the outward manifestation of these. And the warmth is experienced by their senses as warmth but has love within it since it is the outward manifestation of that love. This being so, love is called spiritual warmth and is also the producer of the warmth which man's life possesses, while intelligence is called spiritual light and is also the producer of the light which his life possesses. From this all-inclusive correspondence all other correspondences are derived, for every single thing has regard to good which belongs to love and to truth which belongs to intelligence.