Case Hardened is a gold/blue heat-treat look. The pattern index decides where the blue sits. “Blue Gem” means the playside (what you see in first person) is dominated by blue, not gold.
The community uses tiers (T1–T4) for AK-47 | Case Hardened. T1 indexes are famous and rarely listed; most “cheap Case Hardened” AKs are gold-heavy. Never buy a Blue Gem from a title-only listing.
Same logic applies to Five-SeveN, MAC-10 and some knives with Case Hardened. Dust2pedia shows the skin floor; the gem premium lives on inspect markets.
See also pattern index and overpay.