Why not use pure gold?
Throughout history, we’ve admired and cherished gold for being stable/tarnish-free, conductive, malleable, and most of all, beautiful to behold. However, with few exceptions, most consider pure 24 karat gold to be too soft for jewelry making. Goldsmiths are posed with the challenge of creating alloys, or blends of metal, which embody the valued characteristics of gold while making it durable enough to be wearable and safe for delicate designs and stone-setting.
What makes that pink color?
Rose gold gets its color from copper, used as an alloying metal. Copper and gold work together beautifully. Copper lends a flattering blush to the metallic tone. Gold provides warmth and stabilizes the mix, preventing copper from oxidizing to green. Other common gold alloy metals include nickel and zinc. The blend used determines the resulting color of the gold.