Let us start with white gold.
You’ll find no white gold in the Bank of England’s gold reserve. Pure 24 carat gold is always yellow. There is no such thing as gold that is white.
But jewellery is rarely made from pure gold because it is really quite soft, and pretty expensive. Engagement rings, wedding bands and other jewellery are usually made from an alloy of gold plus other metals.
9 carat gold is 9/24ths gold and 15/24ths other metals
18 carat gold is 18/24ths gold and 6/24ths other metals
22 carat gold is 22/24ths gold and 2/24ths other metals
At the risk of over simplifying things, if the “other metals” in the alloy are copper or silver, the gold remains yellow; whereas if the “other metal” is palladium, it has a “bleaching effect” and the mixture becomes whitish, i.e., “white gold” (or a whiter shade of gold).
Coloured Gold: Gold can take different colours depending on the metals it is mixed with. The different gold hues are generally for the purpose of jewellery. To give you a quick idea here are some different types of gold colours and how they are made:
Rose, Pink, or Red Gold: Gold can take these colours when mixed with copper. The more copper in the alloy, the darker the tone of red that will surface. A common rose gold alloy composition is 18 carat (75% gold) mixed with 25% copper, while a 50/50 mix of gold (12 carat) with copper results in what we would call red gold.
Green Gold: Green gold, otherwise known as electrum, is a natural forming alloy which combines gold and silver. The greenish colour varies depending on the exact mixture.
Blue Gold: 46% gold, 54% indium.
Purple Gold: Also called amethyst gold and violet gold this is made from 80% gold and 20% aluminium.
Black Gold: 75% gold, 25% cobalt.
Purple and White Gold Ring