Revelation 4:3

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.

Ver. 3. Like a jasper and a sardine] God is here resembled (saith Mr Cotton) by three precious stones, holding forth the three persons in Trinity. A jasper having (as they say) a white circle round about it, representing the eternity of the Father. A sardine stone of a fleshy colour representing Jesus Christ, who took our flesh upon him. An emerald, being of a green colour, refreshing the eyes of them that look upon it, representing the Spirit, who is (as the rainbow) a token of fair weather, and is a comfortable refresher, wheresoever he cometh.

And there was a rainbow] Which is signum gratiae et foederis, a sign of grace and of the covenant of mercy, which is always fresh and green about Christ's throne of grace.