The mineral Turquoise gives its name to the colour, but it can also be pale blue. Opaque.
Turquoise is a semi-precious stone, valued in many countries throughout history. It has been called the Turkish stone since the 13C, possibly because the Turks used it so much. It was highly prized by the Aztecs, and it is important to the Navaho people. It has been mined for thousands of years in the Sinai peninsular.
There is a medieval legend that the colour would fade if the stone was in contact with a sick person, but it would regain its colour near someone who was healthy.