All red corundum with gem-quality are considered rubies. However, all other gem quality corundum is considered sapphires. Blue sapphire is simple known as sapphire on the market.’ 

Sapphires get their amazing colors from trace elements such as iron, titanium, chromium, and others. It is possible to find color change in some stones due to traces of vanadium. These gems will show one color in daylight and another under incandescent light.