Allochromatic gems are gems which have been colored by impurities. When they had been completely pure, they'd be colorless. The color of all allochromatic gems is produced by defects. As a result, all color in corundum is caused by defects. Excel in Academics: Primary Yellow sapphire gemstone is no lower https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share