This is all but a description of the glory of God, as he appeared to John in this vision. The jasper stone is famous for its transparency, and variety of colours it offereth to the eye, and may signify the various and infinite perfections of God. The sardine stone is red, and of a bloody colour, which may signify the power, justice, and terror of God. The rainbow was the sign of God's covenant with Noah, signifying his being so far reconciled to the world, as that he would not again destroy it by water, Genesis 9:13. The emerald is green, and pleasant to the eye. So as this vision of God represents God powerful, just, and good, and of various and infinite perfections.
Related Commentaries of Revelation 4:3
Revelation 4:3
3 And he that sat was to look upon like a jasper and a sardine stone: and there was a rainbow round about the throne, in sight like unto an emerald.