Which of the following is NOT a class characteristic of cartridges discharged in guns?

The color of the cartridge casing is indeed not a class characteristic of discharged cartridges. Class characteristics refer to properties that are shared by a group or category of items and can be used to establish a link between evidence and a specific source.

Caliber, for example, represents the diameter of the bullet and is a standard classification relevant to groups of firearms that can fire specific types of ammunition. The firing pin location relates to the design and function of firing pins in different guns, helping to categorize the types of firearms that may have discharged a particular cartridge. Extractor and ejector marks are unique to the mechanics of different firearm models and can help in identifying the specific weapon that fired the cartridge.

In contrast, the color of the cartridge casing can vary based on manufacturing processes and environmental conditions rather than providing a definitive classification that links the cartridge to a specific type or model of firearm. This variability makes it less useful in forensic identification and linkage analysis.