Allochromatic gems are gems which have been coloured by impurities. If they had been entirely pure, they might be colorless. The colour of all allochromatic gems is made by defects. As a result, all colour in corundum is a result of defects. The Srilankan Yellow Sapphire gemstone escalates the understanding https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share