When jewellers speak of coloured gold, they mean coloured gold alloys. Gold Alloys Gold itself is a yellow metallic element but, in its pure form, it is too soft to be used for general jewellery purposes, although there are some cultures which do wear pure gold jewellery, it would need to be heavily made and carefully used. The yellow colour of gold is caused by gold absorbing violet and blue light, but reflecting yellow and red light. It is usual for gold to be mixed with other metals to produce an alloy, which is simply a mixture of two or more metals. Throughout history, most people have preferred the colour of gold jewellery to remain close to that of pure gold itself, and so most jewellery has historically been made using yellow gold alloys.
Most gold alloys are a mixture of gold, copper and silver.
Small amounts of other materials are also added to provide special characteristics. Nickel, zinc, and palladium are common constituents of white gold alloys. It is very simple to produce a gold alloy with a reddish colouration. All that is needed is to increase the proportion of copper in the mixture. To maintain the correct proportion of gold in the alloy, this usually means decreasing the silver content.