The most wanted and rarest pattern you can ever wish on both AK-47 and FiveSeven (and knives) is the blue pattern. There are players willing to pay a lot of money for pattern like this. These blue Case Hardened skins are often called Blue Gems.
1. A knife must be 80% or more coverage of blue/purple on TOP , with minimal gold, silver or pink. Backsides full blue or 75%+ will not be considered a Blue Gem.