Any sapphire that isn't blue is considered a fancy coloured sapphire. Although blue sapphires are more well-known, the various colours available are becoming increasingly popular.
As with other gemstones, the different colours of sapphires are due to trace elements in the crystal structure of the stone. Occasionally, fancy coloured sapphires can display two or even three different colours at one time.
Fancy coloured sapphires are a great option if you're looking for a particular colour of gemstone and want to pair this colour with durabilty.