A gem of the corundum family, yellow sapphire is a twin of ruby and blue sapphire. It is found in yellow, golden, and orange colors, as well as in a colorless variety known as white sapphire. The best gem is said to be of lemon-yellow color. Sapphire is one of the two varieties of Corundum, the other variety being Ruby. Sapphire includes all colors of Corundum except for red stones, which are referred to as Ruby. Sapphire is the most highly valued of the blue gemstones.