Sapphires are actually not all blue- it's just that the blue variety became the most famous due to demand, treatment procedures and historical usage.
Many patrons of old used to associate blue sapphire with the traits of faithfulness, sincerity and truth. Royalty and clergy both admonished themselves with this precious gemstone for centuries. Blue sapphires became the ultimate standard for the vibrant saturations by which every other blue gemstone was compared against.
Britain's most beloved princess- Lady Diana Spencer was proposed to by Prince Charles using a pristine blue sapphire ring, which was passed on to their child Prince William when the time came for him to get married as well.
The most famous source for blue sapphire is the mountainous Kashmir region, where the best qualities were touted as 'Cornflower Blue' sapphires. This trade label became quite famous and is still used today to depict some of the finest sapphire color profiles. The Kashmir mines though did not last for more than a few decades. Quite short in comparison to the long-drawn production timelines of other sources like Australia and Sri Lanka.
Other varieties of corundum aside from blue sapphire and ruby, are all called 'fancy sapphire'. These can be pink, orange, yellow, green, purple, black, or even colorless. Another high end corundum variety is called Padparadscha sapphire- inspired by the pinkish orange colors of a certain lotus flower. This relatively new variant has taken the gem world by storm and can match the finest blue sapphire for value in top market tiers.
It's interesting to note that before the Roman empire, sapphire was not actually known. Many of the gem's iterations in scripts and ancient text actually refer to lapis lazuli, being described as 'the night sky spangled with stars, or spotted with gold'.
