Allochromatic gems are gems which have been colored by impurities. If they were being absolutely pure, they'd be colorless. The colour of all allochromatic gems is made by defects. Consequently, all colour in corundum is a result of defects. Noted for its clarity and shading uniformity, the Burmese Yellow Sapphire https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share