And He who sat there was like a jasper and a sardius stone
in appearance; and behold there was a rainbow around the throne,
in appearance like an emerald.
In a delightful way, John must have panicked at this image because he knew that the same God giving him this vision was the same God who set the rainbow into motion in Genesis when He promised Noah that He would preserve history. Now that rainbow has moved from the ark to around the throne, reminding John that God is able to keep the promises He makes. Those concentric circles around the throne, in those colors, serve as tools of remembrance of the attributes of God.