Color zoning, which forms from growth layers that build up during the formation of the stone, is present in certain sapphires. However, uniformity of color is an important factor in a sapphire's value. Colorless and pale blue sapphires from certain localities may be heat treated to give them an intense blue color. Heat-treatment may also improve the clarity of some sapphires by removing tiny inner inclusions. Sapphire is pleochroic, displaying a lighter and more intense color when viewed at different angles.
Some pleochroic sapphire is blue when viewed at one angle, and purple at a different angle.
A rare variety of sapphire, known as color changing sapphire , exhibits different colors in different light. In natural light, color changing sapphire is blue, but in artificial light, it is violet. This effect is the same phenomenon seen in alexandrite. Sapphire was first synthesized in 1902. The process of creating synthetic sapphire is known as the Verneuil process.