Allochromatic gems are gems which are coloured by impurities. When they were being completely pure, they would be colorless. The colour of all allochromatic gems is produced by defects. Therefore, all colour in corundum is because of defects. Burma has long been renowned for developing a wide array of important https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share