Treyarch has rolled out the Fall Firearms gun skins pack for $20 in the in-game store. While one gun skin is available from buying it, the other one is tucked away via “tiers” in the Black Market which requires players to grind or spend real-world money to bypass. Read the article for the full, detailed explanation.
Source: N4G PC Latest Black Ops 4 Patch Features DLC Containing 2 Gun Skins for , Grinding Still Required