The color separation of the Fold Line from the Cut Line in the structure file is absolutely essential. The designer must define the Fold Line with a unique Spot Color that is distinct from the cut lines. This separation acts as a visual rule for the lithography and die-cutting operator, allowing them to easily distinguish the function of each line and prevent the accidental substitution of creasing rules with cutting blades.

Geometric errors in the Fold Line cause the final packaging to close improperly, which directly impacts the Safe Area. It is precisely these variations in rule thickness and registration errors during printing and die-cutting that amplify the importance of the Safe Area to prevent crucial text from being compromised near the fold line.