Precious stones and pearly gates
Rev 21:18 And the building of the wall of it was of jasper: and the city was pure gold, like unto clear glass.
Pure gold and transparent. As we are to be pure and transparent, free from sin.
1 Pet 1:7 That the trial of your faith, being much more precious than of gold that perisheth, though it be tried with fire, might be found unto praise and honour and glory at the appearing of Jesus Christ:
Rev 3:18 I counsel thee to buy of me gold tried in the fire, that thou mayest be rich; and white raiment, that thou mayest be clothed, and that the shame of thy nakedness do not appear; and anoint thine eyes with eyesalve, that thou mayest see.
The richness is spiritual, not material. There is no use for physical wealth in the spiritual city. All the beauty is to house those beautiful saints, free of sin, who have seen the Lord and are made pure by his forgiveness and grace. Dwelling with them is the most Holy God; the Father and the Son.
Rev 21:19 And the foundations of the wall of the city were garnished with all manner of precious stones. The first foundation was jasper; the second, sapphire; the third, a chalcedony; the fourth, an emerald;
Rev 21:20 The fifth, sardonyx; the sixth, sardius; the seventh, chrysolyte; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst.
The beautiful Holy City was represented symbolically by the breastplate worn by the high priest. Here it is described from God's own design given for it's construction.
Exo 28:15 And thou shalt make the breastplate of judgment with cunning work; after the work of the ephod thou shalt make it; of gold, of blue, and of purple, and of scarlet, and of fine twined linen, shalt thou make it.
Exo 28:16 Foursquare it shall be being doubled; a span shall be the length thereof, and a span shall be the breadth thereof.
Exo 28:17 And thou shalt set in it settings of stones, even four rows of stones: the first row shall be a sardius, a topaz, and a carbuncle: this shall be the first row.
Exo 28:18 And the second row shall be an emerald, a sapphire, and a diamond.
Exo 28:19 And the third row a ligure, an agate, and an amethyst.
Exo 28:20 And the fourth row a beryl, and an onyx, and a jasper: they shall be set in gold in their enclosings.
Exo 28:21 And the stones shall be with the names of the children of Israel, twelve, according to their names, like the engravings of a signet; every one with his name shall they be according to the twelve tribes.
Rev 21:21 And the twelve gates were twelve pearls: every several gate was of one pearl: and the street of the city was pure gold, as it were transparent glass.
The twelve gates, were one pearl for each gate. I see this as a beautiful glowing transparent white in color; but not necessarily round in shape. Everything else seems to be clear and transparent. The stones mentioned each having various hues of colors. Some churches have stained glass windows, that always look their best with the suns light projecting colors into the tabernacle. Heaven will be a beautiful place of colored lights and glory.