Allochromatic gems are gems that are coloured by impurities. When they were being totally pure, they might be colorless. The color of all allochromatic gems is made by defects. As a result, all color in corundum is due to defects. Excel in Lecturers: Unique Yellow sapphire gemstone is not any https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share