Allochromatic gems are gems which have been coloured by impurities. If they ended up fully pure, they'd be colorless. The color of all allochromatic gems is produced by defects. Hence, all color in corundum is a result of defects. Sri Lanka’s Aggressive Edge Sri Lanka’s gem and jewellery value chain https://socialwebnotes.com/story3525178/natural-pukhraj-from-sri-lanka-things-to-know-before-you-buy