The most valuable colors of Sapphire are the cornflower blue Kashmir Sapphire, the very rare, orange-pink Padparadschah and Color Changing Sapphire ( blue in natural light and violet in artificial light ).
All colors of Corundum except red - which is called Ruby- are referred to as Sapphire. Anything other than blue is specified with a prefix color such as "Yellow Sapphire".
Sapphires often contains minor inclusions of tiny slender Rutile needles. When present, these inclusions decrease the transparency of a stone and are known as silk. When in dense, parallel groupings, these inclusions produce asterism and the stone is called "Star Sapphire".