Allochromatic gems are gems that happen to be colored by impurities. Whenever they had been completely pure, they might be colorless. The colour of all allochromatic gems is produced by defects. Thus, all colour in corundum is due to defects. Natural Pukhraj can be a hugely coveted and precious gemstone, https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share