The spoken of rainbow are in Revelation 4 and 10.
The unspoken rainbow but seen is in these verses in chapter 21 about the cosummate New Jerusalem.
The foundations of the wall of the city were adorned with every precious stone: the first foundation was jasper; the second, sapphire; the third, chalcedony; the fourth, emerald; The fifth, sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, topaz; the tenth, chrysoprase; the eleventh, jacinth; the twelfth, amethyst. (Rev. 21:19,20)
The appearance of many colored stones adorning the wall of the New Jerusalem have the appearance of a rainbow.
They precious stones signify transformed human beings into the image of Jesus Christ.
For all who come to Christ are living stones built up into a spiritual house, a holy priesthood of believers.
You yourselves also, as living stones, are being built up as a spiritual house into a holy priesthood to offer up spiritual sacrifices acceptable to God through Jesus Christ. (1 Pet.2:5)
Peter as the leading disciples and apostle of the twelve original disciples was a man transformed.
Christ changed his name from Simon to a stone, meaning he would be transformed to be fit for the buiding of the church.
And I also say to you that you are Peter, [stone] and upon this rock [the revelation of Christ the Son of God] I will build My church, and the gates of Hades shall not prevail against it. (Matt. 16:18)
Peter took the lead among the saved to be transformed into a building stone for God's living dwelling place.
This dwelling place will consummate in the New Jerusalem.
All the believers in eternity will have been transformed to form a protective wall guarding the interests of God the Creator.
Twelve kinds of stones signals perfection in eternity - the number twelve.
The testimony of God's faithfulness in judgment of the world is seen that men and women are not only saved but "metabolically" conformed and transformed in life to the image of Christ as sons of God. (Rom 8:28, 2 Cor., 3:17,18) They form the appearance of a rainbow around the dwelling place of God in humanity in the new universe.
And in the normal church life this transformation should already be taking place.
This is brief.