Here is an interesting New Testament Trinity (Троица Новозаветная / Troitsa Novozavetnaya). It belongs to a subtype of New Testament Trinity icons that we can call the “Royal Doors” subtype.
You can easily see why we may call it the “Royal Doors” subtype — because it has the New Testament Trinity — God the Father, Jesus, and the Holy Spirit as a dove — depicted behind the two panels of the “Royal Doors” — the “Tsar Doors” (Tsarskiy Vrata) that open to the altar in Russian Orthodox churches.
Between the Royal Doors we see the throne represented as an altar table, with Gospel book, cross, and the symbols of the Passion — and you may recall that such a “throne-altar” is a symbol of the second coming of Jesus and the final judgment, as found in icons of the type called the “Preparation of the Throne.”
On the lower part of the doors we see the symbols of the Four Evangelists — Matthew, Mark, Luke and John. And above them at left is a blue cherubim (remember that the plural, though technically inaccurate, is used in Russian icons), and at right a red seraphim. In the West we would of course say a “cherub” and a “seraph.” The tradition developed that Seraphim — being fiery angels close to the throne of God — were to be painted red; Cherubim were painted blue to represent the wind (the blue of the sky), in keeping with 2 Samuel 22:11 (2 Kings 22:11 Septuagint):
И вседе на Херувимы и лете, и явися на крилу ветреню….
I vsede na Kherubimui i lete, i yavisyua na krilu vetreniu ….
“He rode on cherubim and flew; and he appeared on the wings of the wind.”
However we sometimes find that painters did not follow this tradition.
Now keep in mind that in Russian Orthodox churches, the Royal Doors are regarded as a kind of gateway to the heavenly mysteries, because behind them is the altar where the Eucharist is prepared. So here they are seen as the doors to heaven. And as already mentioned, the “throne” as altar with the Gospel book and cross relates to the second coming of Jesus and the final judgment, as we read in the creed known as the “Symbol of Faith” (the Nicene Creed), which could be considered a description of the New Testament Trinity icon type:
“And the third day He rose again, according to the Scriptures, and ascended into Heaven, and sits at the right hand of the Father; and He shall come again with glory to judge the living and the dead; Whose Kingdom shall have no end.”
Note that Jesus has his customary “cross” halo, and God the Father (Lord Sabaoth) his “eight-pointed slava” (slava meaning “glory”) — representing the seven days of Creation and the eighth day — the Day of Eternity.