Allochromatic gems are gems which have been coloured by impurities. Whenever they ended up fully pure, they'd be colorless. The colour of all allochromatic gems is produced by defects. Consequently, all color in corundum is caused by defects. Burma has long been renowned for manufacturing a variety of cherished gemstones, https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share