The most commonly used yellow gold alloys in the jewelry industry, 14k and 18k, contain pure gold that has been alloyed with both copper and silver. The balance of copper and silver proportions result in the metal to reflect a yellow color, however if the proportions of these two alloys are changed the metal’s hue will change. When the copper content is increased and the silver content is decreased, the result is a gold alloy that has a strong red (or pink) tone- rose gold.
When the copper content is decreased and the silver content is increased, the result is a gold alloy with a strong green tone- green gold.
It is important to note that neither rose nor green gold has a lower pure gold content than yellow gold, just a different color.