John Wesley on Revelation 4:3

And he that sat was in appearance - Shone with a visible lustre, like that of sparkling precious stones, such as those which were of old on the high priest's breastplate, and those placed as the foundations of the new Jerusalem, Rev 21:19,20. If there is anything emblematical in the colours of these stones, possibly the jasper, which is transparent and of a glittering white, with an intermixture of beautiful colours, may be a symbol of God's purity, with various other perfections, which shine in all his dispensations. The sardine stone, of a blood - red colour, may be an emblem of his justice, and the vengeance he was about to execute on his enemies. An emerald, being green, may betoken favour to the good; a rainbow, the everlasting covenant. See Gen 9:9. And this being round about the whole breadth of the throne, fixed the distance of those who stood or sat round it.