Au750 refers to gold with a gold content of 75%. If pure gold is 24K, 75% of it is 18K, so au750 is also called 18K gold, and its colors are generally white, yellow and gold pink. Tiffany. Co is the symbol of Tiffany brand, and 750 stands for 18k gold jewelry. Tiffany's Chinese name: Tiffany, the world's top jewelry brand.