4:3 And He who was sitting was like a jasper stone and a sardius in appearance; and there was a raindow around the throne like an emerald in appearance.

And He who was sitting was like a jasper stone and a sardius in appearance;

Here we have two contrasting colors of gems:

Jasper is clear, dazzling and transparent. It is what the new Jerusalem looks like - Revelation 21:11.

Sardius is deep, fiery, flashing red.

For the believer, the brilliance symbolizes the authority to carry out the judgment (from the throne). The red symbolizes Christ's shed blood; the price has been paid.

For the apostate church and unbeliever the brilliance will bring to light the depth of sin, wrong-doing, and denial. The fiery red is the testing of those sins (things of the flesh - wood, hay, straw (1 Corinthians 3:12-17).

Note that "the groom" in the Song of Solomon 5:10 is white and ruddy, the same two colors. He is considered beautiful to look at. Thus, John is amazed at what he sees. John probably recalled this Old Testament passage as he stood there and looked.

From a Jewish perspective, the jasper stone is the last stone of the breastplate (Exodus 28:15-21). The breastplate was worn by the high priest "over his heart when he enters the holy place" (Exodus 28:29-30). This symbolizes the closeness that Christ (as our high priest now (Hebrews 9:11-14)) holds the Jewish people. He is carrying them (and us) right up to the throne if we accept Him.

and there was a RAINBOW AROUND THE THRONE like an emerald in appearance.

This rainbow encircled the throne. A circle is complete and never ending. The rainbow was a symbol of mercy, Genesis 9:13-17, everlasting between God and earth people. He promised never to bring complete physical destruction to mankind (until after the judgment...current heaven and earth pass away).

From physics, a rainbow is formed by the bending of white light into different wavelengths. While all colors appear in an earth rainbow; this rainbow only has an emerald green color. Thus, it is not generated from white light passing through rain/water but most likely is the excited state of atoms which then in turn give off the green light. Green often symbolizes life and fruitfulness.

Lastly, some final thoughts on THE THRONE. It is the focal point of the spiritual realm. Judgment takes place there as well as rewards are given there. Habakkuk prays out of fear that God in His "wrath will remember mercy", Habakkuk 3:1-7. It is this THRONE before which we all will stand!