Gold often comes as an alloy and for that will be of various color. Gold colouring goes from that bright yellow we all know to White, Rose, Pink, Red Gold, Green, Blue, Purple and Black Gold.
Depending on the allow mix, you can derive or metallurgically fabricate colors.
http://goldresource.net/types-of-gold/ illustrates it well.
- White Gold: For gold to take a white color, it must be mixed with a white metal such as nickel, manganese or palladium. Standard White gold is usually 14K of gold (58.5% purity) while the rest is divided as 21% copper, 7.84% zinc, and 12.73% nickel. and White gold can often be rhodium plated to give it a more shiny and white appearance.
- Rose, Pink, Red Gold: Gold can take these colors 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 18K (75% gold) mixed with 25% copper while a 50/50 mix of gold (12K) 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 color varies depending on the exact mixture but back in the 73% gold, 27% silver
- Blue Gold: 46% gold, 54% indium.
- Purple Gold: 80% gold, 20% aluminium.
- Black Gold: 75% gold, 25% cobalt.
http://www.webexhibits.org/causesofcolor/9.html complements it well in talking about gold alloys in saying that metals are coloured because the absorption and re-emission of light are dependent on wavelength. Gold and copper have low reflectivity at short wavelengths, and yellow and red are preferentially reflected, as the colour here suggests. Silver has good reflectivity that does not vary with wavelength, and therefore appears very close to white.