Shades only drops from Zombies that wear backpacks. It also operates differently to other power-ups. Shades occupies the Tactical Grenade slot, and has to be picked up manually by pressing the Use key. It can also be toggled at will, unlike other power-ups.
When the Shades is obtained, the player can wear them. When the Shades are worn, the vision of the player turns black and white. The Shades allow the player to see the red targets around the map. If the player is injured whilst wearing the Shades, the Shades will be dropped form the player's inventory to be picked up again from the floor.