Allochromatic gems are gems that are coloured by impurities. If they ended up wholly pure, they might be colorless. The colour of all allochromatic gems is produced by defects. Therefore, all colour in corundum is brought on by defects. Beware glass-crammed Ceylon Yellow Sapphires. They might appear shiny Nonetheless they https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share